of the Leg of the Crocodile. 329 



tendon, which receives, in particular, the anterior fibres of this 

 enormous muscle, and, passing down the back of the femur, is 

 inserted by a strong common aponeurosis into the outer con- 

 dyle of the femur and into the head of the fibula. This com- 

 mon aponeurosis also gives a partial origin to the gastrocnemius 

 (a, fig. B) and to the plantaris {x, fig. A). 1*81 oz. 



There are two muscles, accessory to this great caudal extensor 

 in their action, which are as follows : — 



12. M. extensori femoris caudali accessorius. Origin : from 

 the fascia covering the great caudal extensor, and by a tendinous 

 head from the quadratus femoris, which is also an accessory to 

 the great caudal. Insertion : into the looped tendon of the 

 semimembranosus already described. 001 oz. 



13. M. quadratus femoris. Origin : posterior, superior, and 

 inner surface of the pubis, near its symphysis. Insertion : into 

 the back of the femur, with the action and position of the 

 quadratus femoris in mammal quadrupeds, and into the tendon 

 of the great caudal extensor. O05 oz. 



The effect of the interlacing of the tendons of the various 

 muscles already described must be to produce simultaneity of 

 action among them, such as I have already endeavoured to de- 

 scribe in my account of the leg of the Ostrich ; and in the pre- 

 sent instance of the Crocodile there seems to be a similar prin- 

 ciple involved. The Crocodile, resting on mud, progresses 

 chiefly by using his hind feet as paddles ; and in this use of 

 them the great caudal extensor of the thigh is the most powerful 

 and important muscle employed. And it seems to me that the 

 simultaneity of action of all parts of the leg, rendered necessary 

 by the employment of so powerful a muscle, is fully secured by 

 the interlacing of the tendons I have described, which renders 

 it impossible for one set of muscles to act without the others 

 being also exerted. 



The remaining muscles of the posterior limb are as follows : — 



14. M. glutseus medius. Origin : from the central part of 

 the ilio-ischiadic surface. Insertion : its tendon passes over the 

 great trochanter, to be inserted into a line down the upper half 

 of the outside of the femur, between the origins of the two por- 

 tions of the vastus externus. 0*06 oz. 



15. M. glutseus minimus. Origin : from the anterior point 

 of the ilium. Insertion : into the inner side of the knee, under 

 the fascia of the rectus femoris. 0*02 oz. 



16. Mm. vastus interims, externus, et crurseus. The vastus 

 externus consists of two distinct muscles, as in the Ostrich. 

 0-22 oz. 



17. M. psoas. This large muscle takes an origin as high as 

 the last rib, and is inserted into the lesser trochanter and the 



