148 PHYSIOLOGICAL SERIES. 



muscles. The biceps has both ischial and femoral heads, 

 of which the latter rises not from the femur but from the 

 deep surface of the femoro-coccygeus. The tensor fasciae 

 latse, gluteus maximus, and femoro-coccygeus, on the 

 other hand, are fused into a single sheet. The sartorius 

 is weak. The muscles of the shank are in comparison 

 with those of the thigh decidedly feeble. The soleus is 

 quite distinct from the gastrocnemii, and has a separate 

 insertion upon the calcaneum. The accessorius, as in 

 other Anteaters and Sloths, is strongly developed. The 

 short extensors of all the toes but v. rise from the dorsum 

 of the foot. O.C. tezkd. 



Windle & Parsons, Proc. Zool. Soc. 1899, p. 990. 



C. 210. Superficial muscles of the right hind-limb of a Three-toed 

 Sloth (Bradypus trldactylus) . The great strength of flexors 

 and adductors, in comparison with extensors previously 

 mentioned in connection with the fore-limb (C. 146), is 

 equally striking in the hind-limb. This feature is specially 

 marked in the flexors of the knee-joint. Below the knee 

 the muscles on either aspect of the limb are fairly equal 

 in size. The flexors of the knee, apart from their size, owe 

 some of their power to the degree (especially marked in the 

 gracilis and biceps) to which their insertions approximate 

 to the distal ends of tibia and fibula. Mention may be made 

 of the following muscles: The gracilis, a remarkably strong 

 double muscle, its two parts are inserted about the middle 

 of the tibia and fibula respectively. The biceps cruris 

 is also double, one portion rising from the tuber ischii, 

 the other from the outer side of the femur. This 

 femoral head is again met with in Man and some few 

 Primates. The semitendinosus and semimembranosus form 

 a practically continuous sheet. The two heads of the gastro- 

 cnemius are separate to their common insertion on the heel ; 

 they cross one another in the lower part of their course. 

 There is no plantaris unless it is represented by the femoral 

 head of the flexor digitorum. The peroneus longus rises 

 partly from the outer condyle of the femur in conjunction 

 with the extensor longus digitorum. The accessorius is 

 very large. 



