310 F. B. Loomis — Osteology and Affinities 



by having the above described interlocking series of concave 

 prezygapophyses and cylindrical postzygapophyses as is typical 

 of Tylopoda generally. While the neural spines only rise to 

 moderate heights, they are wide, thin plates, considerably 

 expanded above. The transverse processes extend, attaining 

 the (for so small a form as S. hitchcocJci) considerable length 

 of 34 mm . 



Sacrum. — The sacrum consists of four fused vertebrae hav- 

 ing a total length of 59 mm and a width of 62 mra . The first of 

 the component vertebrae sends out a stout and much expanded 

 pleurapophysis to receive the ilium. To this is added the 

 smaller but still stout pleurapophysis of the second sacral ver- 

 tebra. These two sacrals are heavy, but the two posterior 

 vertebrae having only to support the tail are reduced and have 

 become very slender. 



Caudal vertebral. — The tail is supported by 14 vertebrae, of 

 which the proximal ones are short and wide with well-marked 

 transverse processes. Beginning with the seventh, however, 

 the vertebrae are without transverse processes, and become 

 approximately cylindrical rods, the last one being but 5 mm long 

 and but l mm in diameter. The whole series measures 170 nun , 

 indicating a tail of moderate length. 



Ribs. — The first of the ribs is short and stocky, while the 

 succeeding eleven are thin and wide (though not so wide as in 

 the living camels), the interval between succeeding ribs being 

 about half the width of the rib itself. A typical rib measures 

 175 mm long by 18 wide. Each rib has two heads rather close 

 together, followed by a narrow abruptly curving neck, and 

 then expands and stretches in a gentle curve toward the 

 sternum. The uncrushed ribs show the body to have been 

 decidedly narrow and moderately deep. The first five ribs 

 w T ere attached directly to the sternum by short calcified costal 

 cartilages; the sixth and seventh by longer calcified cartilages; 

 and the succeeding three are connected by long costal cartilages 

 to each other and indirectly to the sternum ; while the eleventh 

 and twelfth are free ribs. 



Sternum . — The sternum consists of a slender presternum of 

 22 mm length, followed by five wide sternal segments fused to 

 each other. Opposite the point of union of each two segments 

 the margin is expanded and offers an attachment for the 

 costal cartilages. The sixth joint receives the two longer 

 costal cartilages. Finally there is the xiphisternum, a thin 

 expanded lamella of bone extending sume 42 mm behind the 

 rest of the sternum. 



Fore limb. — The scapula is relatively long and narrow, the 

 anterior margin extending upward in a decidedly concave curve, 

 while the posterior margin is bounded by a like though less 



