GREGORY: NOTIJAKCTUS, AN AMERICAN EOCENE PRIMATE 



117 



the cross section of the vertebrse being less angular ; but they are a little more vigorously developed than 

 those of Propithecus, which are very slender cylinders almost without transverse processes. 



The functional significance of these structural details may be elucidated by a brief comparative survey 

 of the musculature of the tail of various mammals. 



Fig. 29. Tail iiiusclcs of inaimriiils. After Cin icr and Laurillarcl. 



yli Castor, lateral view, left side. .4-' The same, dorsal view. 



A'^ The same, ventral view. B Cehus, lateral view, right side. 



Musculature of the Sacral and Caudal Regions. — Cuvier and Laurillard (Recueil de Planches 

 de Myologie) give dissections of the tail of several animals with prehensile tails, such as Cehus, Nasua, 

 Tamandua, and of others, such as the kangaroo, the beaver, and the Orruthorhijiichtis, which ha\'e very 



