48 



not excepting even the second, and are not otherwise remarkable, than for the 

 great breadth of the atlas, which surpasses that of the skull, and for the large 

 and strong spine of the dentata. The dorsal region is characterized by the al- 

 most uniform length and direction of its spines, but is more remarkable for the 

 great capacity of the spinal canal and the concomitant expansion of the neural 

 arches, the vertebrae surpassing in these charE^cters those of the Elephant. The 

 lumbar region is still more peculiar : instead of the row of long and broad trans- 

 verse processes which usually characterize it in the larger Mammalia, a con- 

 tinuous, thin and nearly horizontal plate extends from each side of this short 

 region of the vertebral column, in which plate only the two anterior vertebral in- 

 terspaces are indicated by emarginations. 



Cervical vertebrce. — The atlas* is a transversely oblong, subdepressed, shuttle- 

 shaped bone, perforated by a large, subquadrate aperture for the spinal chord, 

 which is bounded above and below by simple and slightly arched plates of bone, 

 neither of which bear tubercle or spine : the lower plate, representing the body 

 of the vertebra, has a shorter transverse, and a still shorter antero-posterior ex- 

 tent, than the upper or neural plate. The sides of the central aperture are 

 formed by the articular and transverse processes ; the latter are broad and large, 

 and decrease in thickness to their outer convex margins, the posterior rounded 

 angles of which are produced backwards. 



The laminar body of the vertebraf is smooth and convex at its under surface ; 

 the thick anterior margin is straight, and separated by a notch, on each side, 

 from the deep anterior articular cavities : the posterior margin is a little pro- 

 duced in the middle and concave on each side : the upper part of the plate is 

 impressed by the large transversely elliptical surface J, on which the odontoid 

 process plays. The anterior part of the spinal aperture is suddenly widened by 

 two deep lateral excavations §, forming the anterior articular cavities for the oc- 

 cipital condyles. The surface of these cavities is not, as usual, uniformly 

 smooth ; a rough tract, which evidently has not been covered by synovial mem- 

 brane, encroaches on the surface from its inner side. The posterior articular 

 surfaces | are circular, very slightly concave, with their plane looking obliquely 

 inwards and backwards. Between these and the odontoid surface, on the inner 



* PI. VII. figs. 1,2. 3, 4. t Figs. 2, 3 and 4, a. J Figs. 1 and 3./. 



§ Fig. 2. d, d. II Fig. 3. e, e. 



