102 



capacity. Unlike tliat ot" tlie animal just named, it is quite circular, and 

 about 3J inches in diameter. The portion occupied by the spinal cord is 

 absolutely larger than in the mastodon, and it is but slightly defined, from the 

 portion for the pivot of the axis, by slight tubercular elevations for the trans- 

 verse ligament. 



The atlas is proportionately longer than in the mastodon, but is of less 

 width. The inferior arch beneath is nearly flat, and without a hypapophysis, 

 and on each side presents a superficial, rough prominence ["or muscular 

 attachment. The neural ai'ch is comparatively long and narrow, and appears 

 to be devoid of a protuberance. 



The articular concavities for the occipital condyles are deeper and more 

 strongly sloping than in the mastodon. They are separated below by a deep 

 notch at the fore part of the inferior arch. Above, they are removed from 

 each other double the distance. 



The articular facets for the a.xis are ovoidal, slightly concave, and incline 

 at an angle of nearly 45°. They are separated below for a couple of 

 inches by the thick back liorder of the inferior arch of the atlas. Above, 

 they are separated by the long semicircular edge of the neural arch. 



The inferior arch of the atlas-supports a facet for the odontoid process of 

 the axis, which is distinct from the articular flxcets on each side of the latter. 



The transverse processes are unlike those of the elephant and mastodon, 

 and are more like those in ordinary ruminants, &c. The ends are broken 

 off, but they appear as broad, thick plates, extending fore and aft, though not 

 the entire length in either direction. 



The canal for the vertebral artery perforates the transverse jjrocess fore 

 and aft from the back half of the upper to the anterior part of the lower sur- 

 face. As a groove, it then turns upward in advance of the root of the trans- 

 verse process, and is directed inward to a canal perforating the neural arch 

 anteriorly above the position of the articular concavities for the occipital 

 condyles. 



Approximative measurements of the atlas are as follows: 



IncbcB. 



Breadth between the outer edges of the anterior articular concavities (>i| 



Depth of the atlas posteriorly from above downward 4.J 



Breadth between the outer edges of the posterior articular facets . . (>i 



Fore and aft extent of the inferior arch at the middle li 



Length of the atlas laterally 5 



Diameter of spinal foramen from above downward 'A^ 



Diameter of spiual foramen transversely ' ^g 



Breadth fore and aft of transverse processes , 3i 



