69 



the obturator vessels and nerves ; the inner side of which is bounded by a well- 

 marked ridge of bone. 



The ischium presents its usual character in the Edentata, being auchylosed 

 by its broad posterior part with the transverse processes of the posterior sacral 

 vertebrae, and contracting as it bends downwards and inwards to form the pos- 

 terior boundary of the obturator foramen. The inner surface of the ischium is 

 tolerably smooth and even ; its outer surface convex, and presenting a rough 

 tuberosity opposite the broadest part of the outlet of the pelvis. 



The outlet of the pelvis presents an obscurely pentangular form ; its longest 

 and vertical diameter being sixteen inches, its transverse diameter fifteen inches. 

 The upper part of the outlet is formed by the last sacral vertebra : the two 

 upper sides reach from the extremities of the transverse process of the last 

 sacral vertebra to an obtuse projecting part of the ischium, the margin so in- 

 tercepted being slightly concave : the two lower sides of the boundary converge 

 in nearly a straight Une from the before-mentioned processes to the symphysis 

 pubis. 



Caudal Vertehrce. — Of these vertebrae twenty are preserved, beginning with 

 the first, and forming a consecutive and uninterrupted series ; the last consist- 

 ing of the body or centrum only, and, from its small size, — two-thirds of an inch 

 in length, — probably not succeeded by more than one or two others in the living 

 animal. 



The bodies of the caudal vertebrae preserve a nearly equal size to the sixth, 

 and then gradually decrease. The transverse processes of the second caudal are 

 the longest, whence they gradually shorten to the nineteenth, and disappear in 

 the twentieth. They maintain throughout the tail the same antero-posterior ex- 

 tent of their base, but increase in this direction at their extremity in the seventh 

 to the fifteenth vertebrae inclusive. The neural arch progressively decreases in 

 height and breadth from the second caudal. The spinous process, which is an inch 

 and a half in height in the second vertebra, gradually sinks, and disappears in the 

 fifteenth. The oblique processes begin to diminish at the fifth vertebra and disap- 

 pear, — the posterior ones at the fourteenth, — the anterior ones at the eighteenth 

 vertebra. The haemapophyses * retain their primitive separated condition in 



* The inferior vertebral plates forming the vascular arch, or chevron bone. 



