THE VERTEBRAL COLUMN. 23 



but a conical process termed the odontoid, which is flattened above and below, 

 concave and rough from one side to the other on its superior face ; convex 

 in the same direction, and perfectly smooth on its inferior face. The latter 

 represents an articular half-hinge, ^ 13 



around which glides the concave arti- 

 cular surface on the superior face of 

 the body of the atlas. The anterior 

 articular processes are carried to the 

 base and to each side of the odon- j/( 

 toidian pivot, in the shape of two un- 

 dulated facets, which are confounded 

 with the gliding surface of the latter, 

 whose destination has been already 

 noted. The spinous process, very 

 powerful and elongated antero-pos- 

 teriorly, is divided behind into two THE AXIS> OR DENTATA . LATERAL VIEW . 

 roughened lips. The transverse pro- 1? Superior spinous process ; 2, Odontoid pro- 

 cesses are slightly developed, and ter- cess ; 3, Intervertebral foramen, or hole of 

 minate posteriorly in a single tubercle, conjugation; 4, Body; 5, Inferior spinous 

 directed backwards. The anterior P^ ;6^Inferior and superior articu- 

 notches are very deep, and are most 



frequently converted into foramina. This vertebra, although voluminous, 

 is light, in consequence of its containing much spongy substance. In the 

 young animal, the odontoid process and the articular surfaces on each side, 

 constitute two centres, distinct from each other and from the body of the 

 vertebra. After the axis, the cervical vertebrae diminish in length and 

 increase in thickness ; while the obliquity of their articular processes becomes 

 the more pronounced the more distant they are from that vertebra. 



Third, fourth, and fifth. Each of these has, at its transverse processes, 

 two prolongations, one anterior, the other posterior. The inferior face of their 

 bodies exhibits a median spine terminated posteriorly by a tubercle, which 

 gradually increases in volume from the third to the fifth vertebra. 



The third presents, between its anterior and posterior articular processes 

 an almost complete gap ; if its anterior extremity be placed on a horizontal 

 plane, it will touch that plane by its articular and transverse processes and 

 its head. In the fourth, the articular processes are united by a thin, sharp 

 osseous plate, notched only in front. Laid on a horizontal plane, the head 

 remains some distance from it. The fifth is known by the continuous, thick, 

 and rugged lamina which unites the articular processes, and by the tubercle 

 of the inferior spine on the body, which is in shape like the heart on a 

 playing-card. 



Sixth. This is distinguished by the slight prominence of the spinous 

 process, but particularly by the almost total disappearance of the inferior 

 spine, and the presence of a third prolongation, very strong and inclining 

 downwards at its transverse process, a circumstance to which this vertebra 

 owes its designation of tricuspid. 



Seventh. This has received the name of prominens, because its spinous 

 process, terminating in a point, is more distinct than in the preceding 

 vertebrae, the axis excepted. It exhibits, besides: deep imprints, which 

 replace the inferior spine, a concave demi-facet on each side of the posterior 

 cavity for the articulation of the head of the first rib ; a particular disposition 

 of its transverse processes, which are unituberculous ; the complete absence of 

 the vertebral foramen; and, lastly, the depth and width of its notches. 



