62 Zoological Societtj. 



much longer than it is broad, and becoming narrow and rounded at 

 its insertion. 



The biceps cruris consists of two portions, each maintaining a 

 distinct course and having a distinct insertion : one of these may 

 be termed ischio-fbularis, and is inserted into the head of tlieyj- 

 bula; the other may be termed femoro-Jibulnr is ; its insertion is 

 into the outer edge of the Jibula from the head to the middle of the 

 bone, and into the /ascia in front of the leg. The semitendinosus 

 and semimembranosus have the same origins as in the human sub- 

 ject, and the latter muscle a similar insertion ; but the semitetidino- 

 sus separates from it at the lower part of the thigh, and continues 

 fleshy for some distance below the knee-joint ; after which the ten- 

 don expands into a broad strong aponeurosis, which is attached along 

 the anterior and inner aspect of the tibia to within a short distance 

 of its lower extremity. In its insertion, the semitendinosus of the 

 Chimpanzee approaches more nearly to the human type, being im- 

 planted by a narrower tendon in front of the tibia immediately be- 

 neath the insertion of the gracilis ; but both these muscles are 

 inserted lower down than in man. 



Mr. Owen remarked, that the names of these last-mentioned 

 muscles by no means agree with the proportion of tendon found in 

 them either in the Orang or the Chimpanzee, the fleshy portion 

 being in these animals of much greater extent ; — a fact which is in 

 accordance with a law that receives many illustrations from the 

 myology of the Orang Utan, viz. that the extent of the fleshy part 

 of a muscle is in proportion to the quantity of motion it has to 

 produce : and this is generally indicated by the degree of motion 

 allowed by the structure of the joint which is the centre of the mo- 

 tion in question. Thus in the human subject it is very rare that an 

 individual can, by the contraction of the flexors of the leg, bring 

 the heel in contact with the back of the thigh; but in the Orang 

 Utan this action is readily performed, and without the slightest op- 

 position at the knee-joint. 



The tensor vagince Jemoris exists distinctly in the Chimpanzee, but 

 no trace of it was found in the Orang. A more powerful rotator of 

 the thigh inwards exists in both animals in a peculiar muscle, which 

 may be termed invertor Jemoris. It was first discovered by Dr. 

 Traill in the Chitnpanzee ; and its origin, form, and insertion in that 

 animal agree with those which are met with in the Orang Utan. 

 Mr. Owen considers that from its insertion into the under and outer 

 part of the trochanter major, and consequently very near to the 

 centre of motion, it can have little effect in drawing the thigh up 

 towards the body as compared with the power of the proper flexors 

 of the thigh. It appears rather to have reference to that structure 

 of the hip-joint which, in the Orang especially, from the absence of 

 the ligamentum teres, and in the Chimpanzee ,h-Qm the yielding tex- 

 ture of that ligament, permits a greater extent of inward rotation 

 than can be accomplished in man. 



The sarlorius is inserted lower down than in man. The rectus 

 cruris corresponds with the same muscle in the human subject ; but 



the 



