1894.] ANATOMY OP ATHEETJRA ArEICANA. 679 



The scapula is remarkable for the straightness of the axillary 

 border, which always shows more or less of a curve in the other 

 Porcupines. The metacromial process is flat and triangular and 

 fairly broad at its base ; it is situated at the extreme end of the 

 spine, and the acromion is aborted beyond it. This arrangement 

 is the same in Hystrix and Erethizon, but differs from Sphingurus, 

 where the metacromion is some distance from the tip of the 

 acromion. 



The humerus closely resembles that of Hystriv ; it differs from 

 that of the Tree-Porcupines in the patency of the supratrochlear 

 foramen. 



The radius is more arched than in Hystrix, but less so than in 

 the Tree-Porcupines. The grooves for the radial extensors of the 

 wrist and the extensor ossis metacarpi poUicis are well marked. 



In the ulna the lower epiphysis is united to the shaft ; it ends in 

 a well-marked styloid process which fits like a pivot into the 

 cuneiform bone. In adult specimens of Erethizon and Sphingunis 

 the lower epiphysis of the ulna was separate. 



The first row of carpal bones consists of a scapho-lunar, cunei- 

 form, and a large pisiform. The radial sesamoid lies across the 

 pahn and articulates \\ith the scapho-lunar. The bones of the 

 second row are normal except that, owing to the sraallness of the 

 unciform, the 5th metacarpal articulates largely with the cuneiform. 

 The phalanges of the thumb are distinct as they are in Hystrix. 

 In Erethizon and Sphingurus they are fused together. 



The OS innominatum resembles that of Hystrix in the prominence 

 of the anterior and posterior ventral spines (corresponding to the 

 anterior superior and anterior inferior spines of human anatomy), 

 in the length of the symphysis pubis, and in the pyriform 

 shape of the obturator foramen. The iliac surface is narrow 

 and looks downward. In the Tree-Porcupines the iliac surface 

 is broader, tlie spines less marked, the symphysis shorter, and the 

 obturator foramen more rounded. 



The femur of AtJieriira agrees with that of Hystrix and differs 

 from that of the Tree-Porcupines in that the trochanters project 

 more and the digital fossa is deeper. A third (gluteal) trochanter 

 is only present in E'ethizon. 



There are two fabellse in Atherura. 



The tibia, as in all Porcupines, shoves a prominent cnemial 

 crest about the middle of the shin. 



The fibula is broad and flat above but soon becomes prismatic 

 below ; it articulates at both ends with the tibia and below with the 

 astragalus. 



The tarsus shows a calcaneum singularly flattened from above 

 downward, forming a very deep groove for the flexor longus 

 hallucis. 



The navicular, as in all Porcupines, consists of two portions 

 lying side by side ; articulating with the inner one there is a large 

 triangular bone, presumably the prehallux, which is folded under 



