1866.] ON THE ANATOMY OF THE CRESTED AGOUTI. 409 



This muscle is similarly arranged in the Hare and Rabbit, but has 

 the fascia which goes to the tendo Achillis relatively weaker than in 

 the Crested Agouti and the Guinea-pig. 



Sartorius (fig. 4, Sa.). This muscle is very broad and fleshy. It 

 is entirely different in its origin to that of Man, and seems to have 

 for its office the rotation of the limb inwards. Its position (at the 

 origin) somewhat resembles that of the pectineus muscle in the hu- 

 man subject. It arises from the ilio-pectineal eminence and the 

 symphysis pubis, as far as its middle, a portion of the gracilis lying 

 superficial to the posterior part of the origin of the sartorius. It is 

 inserted by a tendinous fascia between the superior point of the elon- 

 gated patella and the head of the tibia. 



This tendinous fascia is in close relation at its insertion with the 

 semimembranosus. A very long superficial femoral artery (fig. 4, Art.) 

 crosses this muscle about its middle. 



In the Guinea-pig this muscle has nearly the same position, rela- 

 tion, and attachments as in D. cristata. It differs considerably in 

 the Rabbit and Hare. In the former of these two, besides having 

 an origin from the ilio-pectineal eminence and slightly from the sym- 

 physis, it has another from the outer side of the anterior superior 

 crest of the ilium, these different origins being connected by a strong 

 fascia. In the Hare the main origin is from the anterior superior 

 spine of the ilium, and but slightly from the ilio-pectineal eminence. 



The gracilis is very powerful, from its extensive insertion, although 

 it is but a moderately thick muscle. It arises (fleshy) from fully 

 the posterior half of the symphysis, and is inserted by a fascia from 

 the head of the tibia as far down as the ankle, the sheet of fascia 

 joining that of the semitendinosus. The two together spread out 

 between the internal malleolus and the tuberosity of the os calcis 

 (fig. 4, Gr.). 



This has a similar origin and insertion in the Rabbit, Hare, and 

 Guinea-pig ; but the fascia which proceeds down the leg is relatively 

 weaker in the two first -mentioned. 



The pectineus arises from the ilio-pectineal eminence and the adjoin- 

 ing brim of the pelvis, covered by the sartorius ; its insertion is into the 

 shaft of the femur, immediately beneath the insertion of the iliacus. 



In the Hare and Rabbit it can hardly be said to be covered by the 

 sartorius, and it is scarcely so in the Guinea-pig. 



The vastus externus is very large, and with an origin from the 

 upper half of the shaft of the femur as high as the rudimentary third 

 trochanter ; the insertion, which is by muscle, is on the outside of 

 the patella, into the tendon common to the extensors of the thigh. 



The vastus internus is small, and has a similar origin and insertion 

 to the preceding, but on the inner side of the shaft of the femur. It 

 arises as high as the tibial trochanter (fig. 4, V.i.~). The vasti are 

 similar in the Guinea-pig and Hare. 



The rectus femoris is equal to the vasti muscles in thickness and 

 bulk. It has the common origin by a double tendon, but a little 

 muscular fibre extends beneath the lowest one ; insertion as usual. 

 In the Guinea-pig there is no marked difference. 



Proc. Zool. Soc— 1866, No. XXVII. 



