92 STRUCTURE AND CLASS mOATION OF BIRDS 



origin of the glutasus quartus and inserted on to the inner 

 face of the femur telow the head. 



Vastus Externus} — This arises fleshily along the greater 

 part of the outer side of the shaft of the femur ; it is fused 

 with the crureus in front, and ends with it upon the patellar 

 ligament. 



Crureus} — This is tendinous on the outer surface at its 

 origin from the neck of the femur ; it also arises from a 

 considerable part of the shaft of the femur and is inserted 

 as has already been described. 



Vastus Internus} — This arises from the inner surface of 

 the shaft of the femur and is inserted on to the tibia along 

 with the tibial insertion of the sartorius. 



Obturator Externus.^ — This is a small deep-lying muscle, 

 which arises from the ischium or the ilium, or even partly 

 from the pubis ; it is inserted on to the trochanter. 



Obturator Internus} — This muscle arises from the mem- 

 brana obturatoria and from the ischium. It is inserted on 

 to head of feraur. Gaerod * laid some classificatory stress 

 upon the shape of this muscle, oval or triangular. 



Gemellus.^ — This is a small fleshy muscle, double or 

 single, surrounding the tendon of insertion of the last. 



Semitendinosus.^ — In Palcumedeathismuscle arisesfleshily 

 from the ilium behind the biceps ; it is half an inch broad, 

 and, after being joined by the small accessory which springs 

 from the femur near its distal end, sends a flat tendinous 

 slip to the semimembranosus. The rest of the tendon of the 

 muscle joins the middle head of the gastrocnemius. The 

 muscle shows considerable variations in its attachments and 

 size. It is completely absent in the owls, hawks, and swifts. 

 The accessory head is absent in kingfishers, many Stegano- 

 podes, Golymbus, &c. 



' ' Femori-tibialiu ' (Gadow). ^ ■ Ischio-femoralis ' (Gadow). 



' 'Obturator' (Gadow). 



■"•' On the Anatomy of Chauna derbiana,' &a., P. Z. S. 1876, p. 195. 



* ' Acoessorii niusculi obturatoris ' (Gadow). 



' ' Caud-ilio-flexorius ' (Gadow). 



