178 Proceedings of the Royal Physical Society. 



II. The Muscles of the Back of the Thigh. 



Biceps flexor cruris, better naraed the flexor cruris 

 lateralis, as there was but one head of origin. 



This arose from the dorsal edge of the ischial tuberosity 

 in conjunction with the semi-tendinosus, between the origins 

 of the inferior gemellus and the semi-membranosus, and con- 

 tiguous to both. As the muscle descended the thigh, it 

 spread out into a broad triangular sheet, which covered the 

 lower third of the outer surface of the thigh. 



It ended in a broad aponeurosis, which w^as attached to 

 the head of the fibula, and the outer side of the head of the 

 tibia, while above and below the osseous attachments it 

 became continuous with the fasciae covering the outer side 

 of the thigh and of the leg. Its fascial insertion in the 

 thigh was behind and below the fascial insertion of gluteus 

 maximus, and the two were very close together. 



The nerve supply was through the great sciatic, and 

 was traced back to the 4th, 5th, and 6th lumbar nerves. 



The biceps has a very constant origin from the ischial 

 tuber, but in most animals the name biceps is a misnomer, 

 as the femoral head is commonly absent. The femoral head 

 is found in the New World howling and spider monkeys 

 and in Anthropoid apes. Its most constant and important 

 insertion is into fascia, and more so in lower monkeys and 

 lemurs than in higher monkeys, where bony insertion becomes 

 more important ; but even in lemurs the bony insertion is 

 in one case the only attachment, while in others the insertion 

 is entirely fascial. I can find no account of insertion into 

 the head of the fibula in any monkey lower than Anthro- 

 poid apes, but in my Hapale an insertion into the head of 

 the fibula, although weak, was undoubtedly present. 



In lemurs (2) the tendon of origin from the ischial tuber 

 is continued into the substance of the muscle, and on its 

 outer side for half its length, and muscle fibres take origin 

 from the tendon in a bipenniform manner. Fibres arising 

 from the outer side of the tendon are inserted into the 

 aponeurosis, connecting biceps with vastus externus. All 

 other fibres radiate and are lost in the fascia of the leg. 



