1888.] NATURAL SCIENCES OF PHILADELPHIA. 151 



Semi-memhranosus, as usual, sends its tibial tendon under the in- 

 ternal lateral ligament, Avhich, in position, is mainly continuous with 

 the peroneus quinti digiti. 



Extensor longus cUgitorum exhibits more surface on the front of 

 the leg than the tibialis anticus, which latter extends under it as a 

 thin sheet. The tendon of origin of the extensor perforates the 

 capsule of the knee joint to rise in front of the outer condyle of the 

 femur. 



Peroneus longus rises partly on the fibula, partly on the tibia, ex- 

 tending its origin under the ex. longus digitorum. 



Plantaris rises as usual from the external femoral condyle in com- 

 mon Avith the gastrocnemius, but contracts no union with that muscle 

 on its way down the leg. In passing over the heel into the foot, it 

 is much less firmly tied to the calcaneum than is the ease in the cat. 



Salens rises almost entirely from the tibia. 



Gastrocnemius. The inner head rises from a pit behind the inter- 

 nal condyle of the femur, extending. up vmder the insertion of the 

 semi-membranosus, and showing no sesamoid bone. The outer head 

 has its origin in common with the plantaris from the femur and 

 sesamoid above the external condyle, sending also a delicate tendi- 

 nous band, g in. wide, over the sesamoid to the patella. 



These two heads extend about half way to the heel and then run 

 out into a common thin aponeurosis, which is joined 2^ in. above 

 the heel by the narrow tendon of the biceps, and then thickening it- 

 self, receives the soleus, as already stated ; on the inner side it be- 

 comes especially thick, forming a distinct cord, which near the heel 

 crosses the tendo Achillis to the outer side. 



In dissecting these muscles I was impressed Avith the smallness of 

 the gastrocnemius in the bear as compared Avith that in the digiti- 

 grade Carnivora, and Avas reminded that I had been much more 

 struck by the same circumstance about a year ago, while dissecting 

 the limbs of the Indian Elephant, in Avhich animal, as is well known, 

 the gastrocnemius is of singularly slight dimensions. The physiolog- 

 ical reason for such a relation in these two plantigrade animals, 

 where the heel does not have to be kept off the ground by a contin- 

 uous muscular exertion, is evident, and I regret that no com- 

 parative Aveights of the masses in the elephant were preserved. 



I, hoAvever, selected a slightly built cat from a number preserved 

 in alcohol at the Biological Laboratory of the University of Penn- 

 sylvania, and Avith it made comparisons in Aveight with the bear. 



