324 ELEMENTARY ANATOMY. [LESS. 



the occiput to the tail end, but also possesses a ventral 

 muscular mass (extending forwards as far as the middle of 

 the thorax), which mass is divisible from above downwards 

 into two antero-posteriorly extended masses together con- 

 stituting, as it were, a ventral (and here sub-vertebral) re- 

 flection of the erector spinse. The same appearance occurs 

 in some Reptiles and in Tailed-Batrachians, where the ventral 

 muscles of the tail .repeat below, the dorsal masses above. 

 But these Batrachian caudal muscles are not sub-vertebral 

 not the continuation backwards of sub-vertebral ones of the 

 trunk, but direct continuations backwards of the abdominal 

 muscles, as is also the case in most Fishes. Muscles of the 

 tail (even in man's own order) may be very extensive, and 



FIG. 292. MUSCLES OF RIGHT HALF OF A TRANSVERSE SECTION OF THE 

 TAIL OF Iguana, showing the separation of the caudal muscular cones from 

 the vertebrae by the intrusion above of a supra -caudal mass from the trunk, 

 and by the intrusion below of the femoro-caudal. 



A , dorsal half of caudal cones ; B, ventral half of caudal cones ; SC, supra-caudal ; 

 FC, femoro-caudal. 



caudal muscles may have attachments such as are indicated 

 by their names pu'bococcygeus, ilio-coccygcus, sacro-coccygeits, 

 and ischio-coccygeus respectively. 



Powerful muscles and complex arrangements of tendons 

 are especially developed in forms which, like the Spider- 

 Monkey, are capable of suspending the entire body by the 

 grasping action of the end of the tail. 



20. The MUSCLES OF THE UPPER EXTREMITY, as might 



be expected, often disappear in those forms in which an upper 

 extremity is wanting. Just, however, as we found in the 

 skeleton that we might have bones of the shoulder girdle 

 without any of those of the arm, so we may have certain of 

 the muscles in question attached to that shoulder girdle 

 though the actual extremity be wanting. Such is the case 

 in sorm Reptiles, e.g. in Angnis fragilis. The muscles may 

 be greatly reduced in size where there is little variety of 

 motion, as in Birds and Cetaceans. No profitable compari- 



