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#21 Ge. Pe.

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Publicado el 18 mayo 2008 - 05:27




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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.


3. The Vertebral Column

(Columna Vertebralis; Spinal Column).



The vertebral column is a flexuous and flexible column, formed of a series of bones called vertebræ.

The vertebræ are thirty-three in number, and are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they occupy; there are seven in the cervical region, twelve in the thoracic, five in the lumbar, five in the sacral, and four in the coccygeal.

This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebræ is, however, very rarely increased or diminished.

The vertebræ in the upper three regions of the column remain distinct throughout life, and are known as true or movable vertebræ; those of the sacral and coccygeal regions, on the other hand, are termed false or fixed vertebræ, because they are united with one another in the adult to form two bones—five forming the upper bone or sacrum, and four the terminal bone or coccyx.

With the exception of the first and second cervical, the true or movable vertebræ present certain common characteristics which are best studied by examining one from the middle of the thoracic region.



3a. General Characteristics of a Vertebra


A typical vertebra consists of two essential parts—viz., an anterior segment, the body, and a posterior part, the vertebral or neural arch; these enclose a foramen, the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair of laminæ, and supports seven processes—viz., four articular, two transverse, and one spinous.




A typical thoracic vertebra, viewed from above.





3a. 1. The Cervical Vertebræ

(Vertebræ Cervicales).



Cervical vertebræ (Fig. 84) are the smallest of the true vertebræ, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen in each transverse process. The first, second, and seventh present exceptional features and must be separately described; the following characteristics are common to the remaining four.




Sagittal section of a lumbar vertebra.





FIG. 84



A cervical vertebra.







Side view of a typical cervical vertebra.








First cervical vertebra, or atlas.









Second cervical vertebra, or epistropheus, from above.







Second cervical vertebra, epistropheus, or axis, from the side.








Seventh cervical vertebra.

The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process, hence the name vertebra prominens.


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#22 Ge. Pe.

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Publicado el 19 mayo 2008 - 05:31






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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.


3. The Vertebral Column



3a. 2. The Thoracic Vertebræ

(Vertebræ Thoracales).



The thoracic vertebræ (Fig. 90) are intermediate in size between those of the cervical and lumbar regions; they increase in size from above downward, the upper vertebræ being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs.



FIG. 90



A thoracic vertebra.








Peculiar thoracic vertebræ.

The first, ninth, tenth, eleventh, and twelfth thoracic vertebræ present certain peculiarities, and must be specially considered.










A lumbar vertebra seen from the side.







3a. 3. The Lumbar Vertebræ

(Vertebræ Lumbales).



The lumbar vertebræ (Figs. 92 and 93) are the largest segments of the movable part of the vertebral column, and can be distinguished by the absence of a foramen in the transverse process, and by the absence of facets on the sides of the body.




FIG. 92



A lumbar vertebra seen from the side.





FIG. 93



A lumbar vertebra from above and behind.







Fifth lumbar vertebra, from above.

The Fifth Lumbar Vertebra is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacrovertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes; and by the thickness of its transverse processes, which spring from the body as well as from the pedicles.



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#23 Ge. Pe.

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Publicado el 21 mayo 2008 - 02:54






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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.


3. The Vertebral Column




3a. 4. The Sacral and Coccygeal Vertebræ


The sacral and coccygeal vertebræ consist at an early period of life of nine separate segments which are united in the adult, so as to form two bones, five entering into the formation of the sacrum, four into that of the coccyx. Sometimes the coccyx consists of five bones; occasionally the number is reduced to three.

The Sacrum (os sacrum).—


The sacrum is a large, triangular bone, situated in the lower part of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones; its upper part or base articulates with the last lumbar vertebra, its apex with the coccyx. It is curved upon itself and placed very obliquely, its base projecting forward and forming the prominent sacrovertebral angle when articulated with the last lumbar vertebra; its central part is projected backward, so as to give increased capacity to the pelvic cavity.

Pelvic Surface (facies pelvina).—


The pelvic surface (Fig. 95) is concave from above downward, and slightly so from side to side. Its middle part is crossed by four transverse ridges, the positions of which correspond with the original planes of separation between the five segments of the bone. The portions of bone intervening between the ridges are the bodies of the sacral vertebræ.



FIG. 95




Sacrum, pelvic surface.





If a sagittal section be made through the center of the sacrum (Fig. 99), the bodies are seen to be united at their circumferences by bone, wide intervals being left centrally, which, in the fresh state, are filled by the intervertebral fibrocartilages. In some bones this union is more complete between the lower than the upper segment.



FIG. 99




Median sagittal section of the sacrum.






Dorsal Surface (facies dorsalis).—


The dorsal surface (Fig. 96) is convex and narrower than the pelvic. In the middle line it displays a crest, the middle sacral crest, surmounted by three or four tubercles, the rudimentary spinous processes of the upper three or four sacral vertebræ.



FIG. 96




Sacrum, dorsal surface.





FIG. 97




Lateral surfaces of sacrum and coccyx.





FIG. 98




Base of sacrum.





The Coccyx (os coccygis).—


The coccyx (Fig. 100) is usually formed of four rudimentary vertebræ; the number may however be increased to five or diminished to three. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. All the segments are destitute of pedicles, laminæ, and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the last three diminish in size from above downward, and are usually fused with one another.



FIG. 100




Coccyx.




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#24 Ge. Pe.

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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.


3. The Vertebral Column




3b. The Vertebral Column as a Whole




The vertebral column is situated in the median line, as the posterior part of the trunk; its average length in the male is about 71 cm. Of this length the cervical part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the sacrum and coccyx 12.5 cm. The female column is about 61 cm. in length.


Curves.—


Viewed laterally (Fig. 111), the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic


FIG. 111




Lateral view of the vertebral column.





4. The Thorax


The skeleton of the thorax or chest (Figs. 112, 113, 114) is an osseo-cartilaginous cage, containing and protecting the principal organs of respiration and circulation. It is conical in shape, being narrow above and broad below, flattened from before backward, and longer behind than in front. It is somewhat reniform on transverse section on account of the projection of the vertebral bodies into the cavity.






FIG. 112




The thorax from in front. (Spalteholz.)







FIG. 113




The thorax from behind. (Spalteholz.)







FIG. 114




The thorax from the right. (Spalteholz.)





4a. The Sternum

(Breast Bone)





The sternum (Figs. 115 to 117) is an elongated, flattened bone, forming the middle portion of the anterior wall of the thorax. Its upper end supports the clavicles, and its margins articulate with the cartilages of the first seven pairs of ribs. It consists of three parts, named from above downward, the manubrium, the body or gladiolus, and the xiphoid process; in early life the body consists of four segments or sternebrœ. In its natural position the inclination of the bone is oblique from above, downward and forward. It is slightly convex in front and concave behind; broad above, becoming narrowed at the point where the manubrium joins the body, after which it again widens a little to below the middle of the body, and then narrows to its lower extremity. Its average length in the adult is about 17 cm., and is rather greater in the male than in the female.



FIG. 115




Anterior surface of sternum and costa cartilages.








FIG. 116




Posterior surface of sternum.








FIG. 117




Lateral border of sternum.



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#25 Ge. Pe.

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Publicado el 27 mayo 2008 - 07:08








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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.


3. The Vertebral Column






4b. The Ribs

(Costæ)



The ribs are elastic arches of bone, which form a large part of the thoracic skeleton. They are twelve in number on either side; but this number may be increased by the development of a cervical or lumbar rib, or may be diminished to eleven. The first seven are connected behind with the vertebral column, and in front, through the intervention of the costal cartilages, with the sternum (Fig. 115); they are called true or vertebro-sternal ribs.


FIG. 115




Anterior surface of sternum and costa cartilages.



Common Characteristics of the Ribs (Figs. 122, 123).—



A rib from the middle of the series should be taken in order to study the common characteristics of these bones.

Each rib has two extremities, a posterior or vertebral, and an anterior or sternal, and an intervening portion—the body or shaft.


FIG. 122




A central rib of the left side. Inferior aspect.






FIG. 123




A central rib of the left side, viewed from behind.





First Rib.—The first rib (Fig. 124) is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward.



FIG. 124




Peculiar ribs.




Second Rib.—The second rib (Fig. 125) is much longer than the first, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked.



FIG. 125




Peculiar ribs.




Tenth Rib.—The tenth rib (Fig. 126) has only a single articular facet on its head.



FIG. 126




Peculiar ribs.




Eleventh and Twelfth Ribs.—The eleventh and twelfth ribs (Figs. 127 and 128) have each a single articular facet on the head, which is of rather large size; they have no necks or tubercles, and are pointed at their anterior ends



FIG. 127




Peculiar ribs





FIG. 128




Peculiar ribs.


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#26 Ge. Pe.

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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.



5. The Skull


The skull is supported on the summit of the vertebral column, and is of an oval shape, wider behind than in front. It is composed of a series of flattened or irregular bones which, with one exception (the mandible), are immovably jointed together. It is divisible into two parts: (1) the cranium, which lodges and protects the brain, consists of eight bones, and (2) the skeleton of the face, of fourteen, as follows:

Skull, 22 bones

Cranium, 8 bones

Occipital.
Two Parietals.
Frontal.
Two Temporals.
Sphenoidal.
Ethmoidal.


Face, 14 bones

Two Nasals.
Two Maxillæ.
Two Lacrimals.
Two Zygomatics.
Two Palatines.
Two Inferior Nasal Conchæ.
Vomer.
Mandible.



In the Basle nomenclature, certain bones developed in association with the nasal capsule, viz., the inferior nasal conchæ, the lacrimals, the nasals, and the vomer, are grouped as cranial and not as facial bones.
The hyoid bone, situated at the root of the tongue and attached to the base of the skull by ligaments, is described in this section.



5a. The Cranial Bones. 1. The Occipital Bone

(Ossa Cranii) & (Os Occipitale).



The occipital bone (Figs. 129, 130), situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal.


FIG. 129




Occipital bone. Outer surface.




FIG. 130




Occipita bone. Inner surface.





FIG. 131




Occipital bone at birth.




5a. 2. The Parietal Bone

(Os Parietale)



The parietal bones form, by their union, the sides and roof of the cranium. Each bone is irregularly quadrilateral in form, and has two surfaces, four borders, and four angles.

Surfaces.—The external surface (Fig. 132) is convex, smooth, and marked near the center by an eminence, the parietal eminence (tuber parietale), which indicates the point where ossification commenced.


FIG. 132





Left parietal bone. Outer surface.




The internal surface (Fig. 133) is concave; it presents depressions corresponding to the cerebral convolutions, and numerous furrows for the ramifications of the middle meningeal vessel.


FIG. 133




Left parietal bone. Inner surface.




5a. 3. The Frontal Bone

(Os Frontale)



The frontal bone resembles a cockle-shell in form, and consists of two portions—a vertical portion, the squama, corresponding with the region of the forehead; and an orbital or horizontal portion, which enters into the formation of the roofs of the orbital and nasal cavities.


Squama (squama frontalis).—Surfaces.—


The external surface (Fig. 134) of this portion is convex and usually exhibits, in the lower part of the middle line, the remains of the frontal or metopic suture; in infancy this suture divides the bone into two, a condition which may persist throughout life.



FIG. 134




Frontal bone. Outer surface.



The internal surface (Fig. 135) of the squama is concave.



FIG. 135




Frontal bone. Inner surface.




Ossification (Fig. 136).—


The frontal bone is ossified in membrane from two primary centers, one for each half, which appear toward the end of the second month of fetal life, one above each supraorbital margin.


FIG. 136




Frontal bone at birth.





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#27 Ge. Pe.

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The Skull



5a. 4. The Temporal Bone

(Os Temporale)


The temporal bones are situated at the sides and base of the skull. Each consists of five parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the styloid process.



The Squama (squama temporalis).—The squama forms the anterior and upper part of the bone, and is scale-like, thin, and translucent.



Surfaces.—

Its outer surface (Fig. 137) is smooth and convex; it affords attachment to the Temporalis muscle, and forms part of the temporal fossa; on its hinder part is a vertical groove for the middle temporal artery.


FIG. 137




Left temporal bone. Outer surface.


The internal surface of the squama (Fig. 138) is concave; it presents depressions corresponding to the convolutions of the temporal lobe of the brain, and grooves for the branches of the middle meningeal vessels.


FIG. 138




Left temporal bone. Inner surface.





Mastoid Portion (pars mastoidea).—

The mastoid portion forms the posterior part of the bone.

Surfaces.—

Its outer surface (Fig. 137) is rough, and gives attachment to the Occipitalis and Auricularis posterior. It is perforated by numerous foramina



FIG. 139





Coronal section of right temporal bone.



The posterior surface (Fig. 138) forms the front part of the posterior fossa of the base of the skull, and is continuous with the inner surface of the mastoid portion


FIG. 138




Left temporal bone. Inner surface.


The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the crista falciformis, into two unequal portions (Fig. 140)


FIG. 140




Diagrammatic view of the fundus of the right internal acoustic meatus. (Testut.)

1. Crista falciformis.
2. Area facialis, with (2’) internal opening of the facial canal.
3. Ridge separating the area facialis from the area cribrosa superior.
4. Area cribrosa superior, with (4’) openings for nerve filaments.
5. Anterior inferior cribriform area, with (5’) the tractus spiralis foraminosus, and (5’’) the canalis centralis of the cochlea.
6. Ridge separating the tractus spiralis foraminosus from the area cribrosa media.
7. Area cribrosa media, with (7’) orifices for nerves to saccule.
8. Foramen singulare.



The inferior surface (Fig. 141) is rough and irregular, and forms part of the exterior of the base of the skull.


FIG. 141




Left temporal bone. Inferior surface.


Styloid Procéss (processus styloideus).—

The styloid process is slender, pointed, and of varying length; it projects downward and forward, from the under surface of the temporal bone. Its proximal part (tympanohyal) is ensheathed by the vaginal process of the tympanic portion, while its distal part (stylohyal) gives attachment to the stylohyoid and stylomandibular ligaments, and to the Styloglossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament extends from the apex of the process to the lesser cornu of the hyoid bone, and in some instances is partially, in others completely, ossified.

Structure.—The structure of the squama is like that of the other cranial bones: the mastoid portion is spongy, and the petrous portion dense and hard.


FIG. 142




The three principal parts of the tempora bone at birth.

1. Outer surface of petromastoid part.
2. Outer surface of tympanic ring.
3. Inner surface of squama.




FIG. 143




Temporal bone at birth. Outer aspect.




FIG. 144




Temporal bone at birth. Inner aspect.




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#28 Ge. Pe.

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The Skull



5a. 5. The Sphenoid Bone

(Os Sphenoidale)



The sphenoid bone is situated at the base of the skull in front of the temporals and basilar part of the occipital. It somewhat resembles a bat with its wings extended, and is divided into a median portion or body, two great and two small wings extending outward from the sides of the body, and two pterygoid processes which project from it below.


The superior surface of the body (Fig. 145) presents in front a prominent spine, the ethmoidal spine, for articulation with the cribriform plate of the ethmoid.



FIG. 145




Sphenoid bone. Upper surface.



The lateral surfaces of the body are united with the great wings and the medial pterygoid plates. Above the attachment of each great wing is a broad groove, curved something like the italic letter f; it lodges the internal carotid artery and the cavernous sinus, and is named the carotid groove. Along the posterior part of the lateral margin of this groove, in the angle between the body and great wing, is a ridge of bone, called the lingula.

The posterior surface, quadrilateral in form (Fig. 147), is joined, during infancy and adolescence, to the basilar part of the occipital bone by a plate of cartilage. Between the eighteenth and twenty-fifth years this becomes ossified, ossification commencing above and extending downward.

The anterior surface of the body (Fig. 146) presents, in the middle line, a vertical crest, the sphenoidal crest, which articulates with the perpendicular plate of the ethmoid, and forms part of the septum of the nose. On either side of the crest is an irregular opening leading into the corresponding sphenoidal air sinus.


FIG. 146




Sphenoid bone. Anterior and inferior surfaces.





FIG. 147





Sphenoid bone. Upper and posterior surfaces.




Ossification.—


Until the seventh or eighth month of fetal life the body of the sphenoid consists of two parts, viz., one in front of the tuberculum sellæ, the presphenoid, with which the small wings are continuous; the other, comprising the sella turcica and dorsum sellæ, the postsphenoid, with which are associated the great wings, and pterygoid processes. The greater part of the bone is ossified in cartilage. There are fourteen centers in all, six for the presphenoid and eight for the postsphenoid.


The presphenoid is united to the postsphenoid about the eighth month, and at birth the bone is in three pieces (Fig. 148).


FIG. 148




Sphenoid bone at birth. Posterior aspect.




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The Skull




5a. 6. Ethmoid bone

(Os Ethmoidale)



The ethmoid bone is exceedingly light and spongy, and cubical in shape; it is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities. It consists of four parts: a horizontal or cribriform plate, forming part of the base of the cranium; a perpendicular plate, constituting part of the nasal septum; and two lateral masses or labyrinths.

Cribiform Plate (lamina cribrosa; horizontal lamina).—


The cribriform plate (Fig. 149) is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities.


FIG. 149




Ethmoid bone from above.


Perpendicular Plate (lamina perpendicularis; vertical plate).—The perpendicular plate (Figs. 150, 151) is a thin, flattened lamina, polygonal in form, which descends from the under surface of the cribriform plate, and assists in forming the septum of the nose; it is generally deflected a little to one or other side.


FIG. 150




Perpendicular plate of ethmoid. Shown by removing the right labyrinth.




FIG. 151




Ethmoid bone from behind.




The upper surface of the labyrinth (Fig. 149) presents a number of half-broken cells, the walls of which are completed, in the articulated skull, by the edges of the ethmoidal notch of the frontal bone.
The lateral surface (Fig. 152) is formed of a thin, smooth, oblong plate, the lamina papyracea (os planum)



FIG. 152




Ethmoid bone from the right side.




The medial surface of the labyrinth (Fig. 153) forms part of the lateral wall of the corresponding nasal cavity. It consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, the middle nasal concha.



FIG. 153




Lateral wall of nasal cavity, showing ethmoid bone in position.



5b. The Facial Bones.

1. The Nasal Bones

(Ossa Faciei) & (Ossa Nasalia)



The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, “the bridge” of the nose (Fig. 190). Each has two surfaces and four borders.


FIG. 190




The skull from the front.



Surfaces.—

The outer surface (Fig. 155) is concavoconvex from above downward, convex from side to side; it is covered by the Procerus and Compressor naris, and perforated about its center by a foramen, for the transmission of a small vein. The inner surface (Fig. 156) is concave from side to side, and is traversed from above downward, by a groove for the passage of a branch of the nasociliary nerve.


FIG. 154




Articulation of nasal and lacrimal bones with maxilla.



FIG. 155




Right nasal bone. Outer surface.





FIG. 156




Right nasal bone. Inner surface.



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The Skull


5b. 2. The Maxillæ (Upper Jaw)


The maxillæ are the largest bones of the face, excepting the mandible, and form, by their union, the whole of the upper jaw. Each assists in forming the boundaries of three cavities, viz., the roof of the mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the formation of two fossæ, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary.

Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and palatine




Surfaces.—

The anterior surface (Fig. 157) is directed forward and lateralward.

The infratemporal surface (Fig. 157) is convex, directed backward and lateralward, and forms part of the infratemporal fossa


The orbital surface (Fig. 157) is smooth and triangular, and forms the greater part of the floor of the orbit


FIG. 157




Left maxilla. Outer surface.





The nasal surface (Fig. 158) presents a large, irregular opening leading into the maxillary sinus



FIG. 158




Left maxilla. Nasal surface.



The Maxillary Sinus or Antrum of Highmore (sinus maxillaris).—

The maxillary sinus is a large pyramidal cavity, within the body of the maxilla: its apex, directed lateralward, is formed by the zygomatic process


FIG. 159




Left maxillary sinus opened from the exterior.




The Palatine Process (processus palatinus; palatal process).—

The palatine process, thick and strong, is horizontal and projects medialward from the nasal surface of the bone. It forms a considerable part of the floor of the nose and the roof of the mouth and is much thicker in front than behind. Its inferior surface (Fig. 160) is concave, rough and uneven, and forms, with the palatine process of the opposite bone, the anterior three-fourths of the hard plate.


FIG. 160




The bony palate and alveolar arch.




FIG. 161




Anterior surface of maxilla at birth.





FIG. 162




Inferior surface of maxilla at birth.




5b. 3. The Lacrimal Bone

(Os Lacrimale)



The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit (Fig. 164). It has two surfaces and four borders.


FIG. 164




Left zygomatic bone in situ.



Surfaces.—The lateral or orbital surface (Fig. 163) is divided by a vertical ridge, the posterior lacrimal crest, into two parts. In front of this crest is a longitudinal groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites with the frontal process of the maxilla, and the lacrimal fossa is thus completed


FIG. 163




Left lacrimal bone. Orbital surface. Enlarged.




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#31 Ge. Pe.

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Esta fina construccion ósea del cráneo, da que pensar cuando uno piensa en deportes como el boxeo, o en las películas de acción con fuertes golpes en la cara donde los que lo reciben siguen como si nada...

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Henry Gray (1821–1865). Anatomy of the Human Body. 1918.



The Skull




5b. 4. The Zygomatic Bone

(Os Zygomaticum; Malar Bone)



The zygomatic bone is small and quadrangular, and is situated at the upper and lateral part of the face: it forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal and infratemporal fossæ (Fig. 164). It presents a malar and a temporal surface; four processes, the frontosphenoidal, orbital, maxillary, and temporal; and four borders.


FIG. 164




Left zygomatic bone in situ.




Surfaces.—

The malar surface (Fig. 165) is convex and perforated near its center by a small aperture, the zygomaticofacial foramen, for the passage of the zygomaticofacial nerve and vessels; below this foramen is a slight elevation, which gives origin to the Zygomaticus.

The temporal surface (Fig. 166), directed backward and medialward, is concave, presenting medially a rough, triangular area, for articulation with the maxilla, and laterally a smooth, concave surface, the upper part of which forms the anterior boundary of the temporal fossa, the lower a part of the infratemporal fossa. Near the center of this surface is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve.


FIG. 165




Left zygomatic bone. Malar surface.




FIG. 166




Left zygomatic bone. Temporal surface.




Articulations.—

The zygomatic articulates with four bones: the frontal, sphenoidal, temporal, and maxilla.



FIG. 167




Articulation of left palatine bone with maxilla.






5b. 5. The Palatine Bone

(Os Palatinum; Palate Bone)



The palatine bone is situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid (Fig. 167).



FIG. 167




Articulation of left palatine bone with maxilla.





The Horizontal Part (pars horizontalis; horizontal plate) (Figs. 168, 169).—The horizontal part is quadrilateral, and has two surfaces and four borders.



FIG. 168




Left palatine bone. Nasal aspect. Enlarged.




FIG. 169




Left palatine bone. Posterior aspect. Enlarged.




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The Skull






5b. 6. The Inferior Nasal Concha

(Concha Nasalis Inferior; Inferior Turbinated Bone)



The inferior nasal concha extends horizontally along the lateral wall of the nasal cavity (Fig. 170) and consists of a lamina of spongy bone, curled upon itself like a scroll. It has two surfaces, two borders, and two extremities.

The medial surface (Fig. 171) is convex, perforated by numerous apertures, and traversed by longitudinal grooves for the lodgement of vessels. The lateral surface is concave (Fig. 172), and forms part of the inferior meatus. The lateral surface is concave (Fig. 172), and forms part of the inferior meatus.



FIG. 170




Lateral wall of right nasal cavity showing inferior concha in situ.





FIG. 171




Right inferior nasal concha. Medial surface.





FIG. 172




Right inferior nasal concha. Lateral surface.





5b. 7. The Vomer


The vomer is situated in the median plane, but its anterior portion is frequently bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal septum (Fig. 173); it has two surfaces and four borders. The surfaces (Fig. 174) are marked by small furrows for blood-vessels, and on each is the nasopalatine groove, which runs obliquely downward and forward, and lodges the nasopalatine nerve and vessels.



FIG. 173




Median wall of left nasal cavity showing vomer in situ.




FIG. 174




The vomer.





FIG. 175




Vomer of infant.




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The Skull




5b. 8. The Mandible (Lower Jaw)

(Inferior Maxillary Bone)



The mandible, the largest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles.

The Body (corpus mandibulæ).—


The body is curved somewhat like a horseshoe and has two surfaces and two borders.


Surfaces.—


The external surface (Fig. 176) is marked in the median line by a faint ridge, indicating the symphysis or line of junction of the two pieces of which the bone is composed at an early period of life.



FIG. 176




Mandible. Outer surface. Side view.




The internal surface (Fig. 177) is concave from side to side



FIG. 177




Mandible. Inner surface. Side view.



The Ramus (ramus mandibulæ; perpendicular portion).—

The ramus is quadrilateral in shape, and has two surfaces, four borders, and two processes.




Ossification takes place in the membrane covering the outer surface of the ventral end of Meckel’s cartilage (Figs. 178 to 181), and each half of the bone is formed from a single center which appears, near the mental foramen, about the sixth week of fetal life.



FIG. 178




Mandible of human embryo 24 mm. long. Outer aspect. (From model by Low.)





FIG. 179




Mandible of human embryo 24 mm. long. Inner aspect. (From model by Low.)





FIG. 180




Mandible of human embryo 95 mm. long. Outer aspect. Nuclei of cartilage stippled. (From model by Low.)



Changes Produced in the Mandible.


FIG. 182




At birth.





FIG. 183




In childhood.




FIG. 184




In the adult.




FIG. 185




In old age. Side view of the mandible at different periods of life





5b. 9. The Hyoid Bone

(Os Hyoideum; Lingual Bone)



The hyoid bone is shaped like a horseshoe, and is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments. It consists of five segments, viz., a body, two greater cornua, and two lesser cornua.



FIG. 186




Hyoid bone. Anterior surface. Enlarged.




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The Skull




5c. The Exterior of the Skull


The skull as a whole may be viewed from different points, and the views so obtained are termed the normæ of the skull; thus, it may be examined from above (norma verticalis), from below (norma basalis), from the side (norma lateralis), from behind (norma occipitalis), or from the front (norma frontalis).


Norma Basalis (Fig. 187).—


The inferior surface of the base of the skull, exclusive of the mandible, is bounded in front by the incisor teeth in the maxillæ; behind, by the superior nuchal lines of the occipital; and laterally by the alveolar arch, the lower border of the zygomatic bone, the zygomatic arch and an imaginary line extending from it to the mastoid process and extremity of the superior nuchal line of the occipital.



FIG. 187




Base of skull. Inferior surface.




Norma Lateralis (Fig. 188).—


When viewed from the side the skull is seen to consist of the cranium above and behind, and of the face below and in front.



FIG. 188




Side view of the skull.




The Infratemporal Fossa (fossa infratemporalis; zygomatic fossa) (Fig. 189).—


The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch.



FIG. 189




Left infratemporal fossa.




Norma Frontalis (Fig. 190).—



When viewed from the front the skull exhibits a somewhat oval outline, limited above by the frontal bone, below by the body of the mandible, and laterally by the zygomatic bones and the mandibular rami.



The Orbits (orbitæ) (Fig. 190).—


The orbits are two quadrilateral pyramidal cavities, situated at the upper and anterior part of the face, their bases being directed forward and lateralward, and their apices backward and medialward, so that their long axes, if continued backward, would meet over the body of the sphenoid. Each presents for examination a roof, a floor, a medial and a lateral wall, a base, and an apex.


FIG. 190




The skull from the front.





FIG. 191




Horizontal section of nasal and orbital cavities.





The medial wall (Fig. 192) is nearly vertical, and is formed from before backward by the frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and a small part of the body of the sphenoid in front of the optic foramen.



FIG. 192




Medial wall of left orbit.



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The Skull



5d. The Interior of the Skull



Inner Surface of the Skull-cap.—


The inner surface of the skull-cap is concave and presents depressions for the convolutions of the cerebrum, together with numerous furrows for the lodgement of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several depressions for the arachnoid granulations, and at its back part, the openings of the parietal foramina when these are present. It is crossed, in front, by the coronal suture, and behind by the lambdoidal, while the sagittal lies in the medial plane between the parietal bones.


Upper Surface of the Base of the Skull (Fig. 193).—

The upper surface of the base of the skull or floor of the cranial cavity presents three fossæ, called the anterior, middle, and posterior cranial fossæ.


FIG. 193




Base of the skull. Upper surface.




FIG. 194




Sagittal section of skull.




The roof (Figs. 195, 196) is horizontal in its central part, but slopes downward in front and behind; it is formed in front by the nasal bone and the spine of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid are the foramina for the olfactory nerves, and on the posterior part of the roof is the opening into the sphenoidal sinus.


FIG. 195




Medial wall of left nasal fossa.





FIG. 196




Roof, floor, and lateral wall of left nasal cavity.




The Anterior Nasal Aperture (Fig. 181) is a heart-shaped or pyriform opening, whose long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral and alar cartilages of the nose.



FIG. 181




Mandible of human embryo 95 mm. long. Inner aspect. Nuclei of cartilage stippled. (From model by Low.)




Differences in the Skull Due to AgeAt birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half in the adult.

The frontal and parietal eminences are prominent, and the greatest width of the skull is at the level of the latter; on the other hand, the glabella, superciliary arches, and mastoid processes are not developed. Ossification of the skull bones is not completed, and many of them, e. g., the occipital, temporals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified membranous intervals, termed fontanelles, are seen at the angles of the parietal bones; these fontanelles are six in number: two, an anterior and a posterior, are situated in the middle line, and two, an antero-lateral and a postero-lateral, on either side.

The anterior or bregmatic fontanelle (Fig. 197) is the largest, and is placed at the junction of the sagittal, coronal, and frontal sutures; it is lozenge-shaped, and measures about 4 cm. in its antero-posterior and 2.5 cm. in its transverse diameter. The posterior fontanelle is triangular in form and is situated at the junction of the sagittal and lambdoidal sutures. The lateral fontanelles (Fig. 198) are small, irregular in shape, and correspond respectively with the sphenoidal and mastoid angles of the parietal bones.


FIG. 197




Skull at birth, showing frontal and occipital fonticuli.




FIG. 198




Skull at birth, showing sphenoidal and mastoid fonticuli.





FIG. 199




The premaxilla and its sutures. (After Albrecht.)




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6. The Extremities



The bones by which the upper and lower limbs are attached to the trunk constitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle of the superior extremity is formed by the scapulæ and clavicles, and is imperfect in front and behind. In front, however, it is completed by the upper end of the sternum, with which the medial ends of the clavicles articulate. Behind, it is widely imperfect, the scapulæ being connected to the trunk by muscles only. The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, which articulate with each other in front, at the symphysis pubis. It is imperfect behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, with the sacrum, is a complete ring, massive and comparatively rigid, in marked contrast to the lightness and mobility of the shoulder girdle.


6a. The Bones of the Upper Extremity. 1. The Clavicle

(Ossa Extremitatis Superioris) & (Clavicula; Collar Bone)



The clavicle (Figs. 200, 201) forms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter f, and placed nearly horizontally at the upper and anterior part of the thorax, immediately above the first rib.


FIG. 200




Left clavicle. Superior surface.




FIG. 201




Left clavicle. Inferior surface.




6a. 2. The Scapula (Shoulder Blade)

(Shoulder Blade)



The scapula forms the posterior part of the shoulder girdle. It is a flat, triangular bone, with two surfaces, three borders, and three angles.


Surfaces.—The costal or ventral surface (Fig. 202) presents a broad concavity, the subscapular fossa.


FIG. 202




Left scapula. Costal surface.




The dorsal surface (Fig. 203) is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinatous fossa, and that below it the infraspinatous fossa.


FIG. 203




Left scapula. Dorsal surface.




FIG. 204




Posterior view of the thorax and shoulder girdle. (Morris.)




FIG. 205




Left scapula. Lateral view.




FIG. 206




Plan of ossification of the scapula. From seven centers.








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6a. 3. The Humerus   (Arm Bone)


   The humerus (Figs. 207, 208) is the longest and largest bone of the upper extremity; it is divisible into a body and two extremities.    




  Imagen enviada  



FIG. 207


Left humerus. Anterior view.





    

  Imagen enviada  





FIG. 208


Left humerus. Posterior view.


      Structure.—  The extremities consist of cancellous tissue, covered with a thin, compact layer (Fig. 209); the body is composed of a cylinder of compact tissue, thicker at the center than toward the extremities, and contains a large medullary canal which extends along its whole length.   



   

Imagen enviada  

FIG. 209  


Longitudinal section of head of left humerus.


     Ossification (Figs. 210, 211).—  



The humerus is ossified from eight centers, one for each of the following parts: the body, the head, the greater tubercle, the lesser tubercle, the capitulum, the trochlea, and one for each epicondyle.    





 Imagen enviada  


FIG. 210 


Plan of ossification of the humerus.



    

  Imagen enviada  



FIG. 211


Epiphysial lines of humerus in a young adult. Anterior aspect.



The lines of attachment of the articular capsules are in blue.   

 

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6. The Extremities




6a. 4. The Ulna

(Elbow Bone) 56



The ulna (Figs. 212, 213) is a long bone, prismatic in form, placed at the medial side of the forearm, parallel with the radius. It is divisible into a body and two extremities. Its upper extremity, of great thickness and strength, forms a large part of the elbow-joint; the bone diminishes in size from above downward, its lower extremity being very small, and excluded from the wrist-joint by the interposition of an articular disk.


The Upper Extremity (proximal extremity) (Fig. 212).—The upper extremity presents two curved processes, the olecranon and the coronoid process; and two concave, articular cavities, the semilunar and radial notches.


FIG. 212





Upper extremity of left ulna. Lateral aspect.





FIG. 213





Bones of left forearm. Anterior aspect.





FIG. 214





Bones of left forearm. Posterior aspect.





Ossification (Figs. 215, 216).—

The ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone. At birth the ends are cartilaginous. About the fourth year, a center appears in the middle of the head, and soon extends into the styloid process. About the tenth year, a center appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year.


FIG. 215




Plan of ossification of the ulna. From three centers.





FIG. 216





Epiphysial lines of ulna in a young adult. Lateral aspect.
The lines of attachment of the articular capsules are in blue.





6a. 5. The Radius


The radius (Figs. 213, 214) is situated on the lateral side of the ulna, which exceeds it in length and size. Its upper end is small, and forms only a small part of the elbow-joint; but its lower end is large, and forms the chief part of the wrist-joint. It is a long bone, prismatic in form and slightly curved longitudinally. It has a body and two extremities.




FIG. 213





Bones of left forearm. Anterior aspect.





FIG. 214






Ossification (Figs. 217, 218).—

The radius is ossified from three centers: one for the body, and one for either extremity.


FIG. 217





Plan of ossification of the radius. From three centers.





FIG. 218





Epiphysial lines of radius in a young adult. Anterior aspect.
The line of attachment of the articular capsule of the wrist-joint is in blue.




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6. The Extremities





6b. The Hand.



1. The Carpus



The skeleton of the hand (Figs. 219, 220) is subdivided into three segments: the carpus or wrist bones; the metacarpus or bones of the palm; and the phalanges or bones of the digits.


The Carpus (Ossa Carpi)



The carpal bones, eight in number, are arranged in two rows. Those of the proximal row, from the radial to the ulnar side, are named the navicular, lunate, triangular, and pisiform; those of the distal row, in the same order, are named the greater multangular, lesser multangular, capitate, and hamate.

Common Characteristics of the Carpal Bones.—

Each bone (excepting the pisiform) presents six surfaces. Of these the volar or anterior and the dorsal or posterior surfaces are rough, for ligamentous attachment; the dorsal surfaces being the broader, except in the navicular and lunate. The superior or proximal, and inferior or distal surfaces are articular, the superior generally convex, the inferior concave; the medial and lateral surfaces are also articular where they are in contact with contiguous bones, otherwise they are rough and tuberculated. The structure in all is similar, viz., cancellous tissue enclosed in a layer of compact bone.


FIG. 219





Bones of the left hand. Volar surface.




FIG. 220





Bones of the left hand. Dorsal surface.




Bones of the Proximal Row (upper row).—



The Navicular Bone (os naviculare manus; scaphoid bone) (Fig. 221).

The navicular bone is the largest bone of the proximal row, and has received its name from its fancied resemblance to a boat.


FIG. 221




The left navicular bone.



The Lunate Bone (os lunatum; semilunar bone) (Fig. 222).—

The lunate bone may be distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row of the carpus, between the navicular and triangular.


FIG. 222




The left lunate bone.




The Triangular Bone (os triquetum; cuneiform bone) (Fig. 223).—

The triangular bone may be distinguished by its pyramidal shape, and by an oval isolated facet for articulation with the pisiform bone. It is situated at the upper and ulnar side of the carpus



FIG. 223





The left triangular bone.




The Pisiform Bone (os pisiforme) (Fig. 224).—

The pisiform bone may be known by its small size, and by its presenting a single articular facet. It is situated on a plane anterior to the other carpal bones and is spheroidal in form.


FIG. 224





The left pisiform bone





Bones of the Distal Row (lower row).—


The Greater Multangular Bone (os multangulum majus; trapezium) (Fig. 225).—

The greater multangular bone may be distinguished by a deep groove on its volar surface. It is situated at the radial side of the carpus, between the navicular and the first metacarpal bone.


FIG. 225





The left greater multangular bone.




The Lesser Multangular Bone (os multangulum minus; trapezoid bone) (Fig. 226).—

The lesser multangular is the smallest bone in the distal row. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the volar surface; and by its having four articular facets touching each other, and separated by sharp edges.


FIG. 226





The left lesser multangular bone.




The Capitate Bone (os capitatum; os magnum) (Fig. 227).—

The capitate bone is the largest of the carpal bones, and occupies the center of the wrist. It presents, above, a rounded portion or head, which is received into the concavity formed by the navicular and lunate; a constricted portion or neck; and below this, the body.



FIG. 227





The left capitate bone.




The Hamate Bone (os hamatum; unciform bone) (Fig. 228).—

The hamate bone may be readily distinguished by its wedge-shaped form, and the hook-like process which projects from its volar surface. It is situated at the medial and lower angle of the carpus, with its base downward, resting on the fourth and fifth metacarpal bones, and its apex directed upward and lateralward.


FIG. 228





The left hamate bone.




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6. The Extremities




6b. The Hand.



6b. 2. The Metacarpus


The metacarpus consists of five cylindrical bones which are numbered from the lateral side (ossa metacarpalia I-V); each consists of a body and two extremities.


Characteristics of the Individual Metacarpal Bones.—

The First Metacarpal Bone (os metacarpale I; metacarpal bone of the thumb) (Fig. 229) is shorter and stouter than the others, diverges to a greater degree from the carpus, and its volar surface is directed toward the palm.


FIG. 229






The first metacarpal. (Left.)



The Second Metacarpal Bone (os metacarpale II; metacarpal bone of the index finger) (Fig. 230) is the longest, and its base the largest, of the four remaining bones.


FIG. 230






The second metacarpal. (Left.)




The Third Metacarpal Bone (os metacarpale III; metacarpal bone of the middle finger) (Fig. 231) is a little smaller than the second.


FIG. 231




The third metacarpal. (Left.)




The Fourth Metacarpal Bone (os metacarpale IV; metacarpal bone of the ring finger) (Fig. 232) is shorter and smaller than the third.


FIG. 232




The fourth metacarpal. (Left.)



The Fifth Metacarpal Bone (os metacarpale V; metacarpal bone of the little finger) (Fig. 233) presents on its base one facet on its superior surface, which is concavo-convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal.


FIG. 233




The fifth metacarpal. (Left.)


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