98 STRUCTURE AND CLASSIFICATION OF BIRDS 



In Podiceps, according to GADOW, there is no branch to the 

 flexor tendon, the tendon of insertion -ending at the ankle. 



Peroneus Profundus. This muscle arises from the lower 

 part of the tibia, and is inserted on to the outer side of the 

 ankle. It is completely absent in such birds as Ciconia, 

 Otis, &.c. 



Gastrocnemius. This great muscle occupies the greater 

 part of the back of the leg. It has three heads, of which 

 the outer arises from the outer condyle of the femur, and 

 from the ligament which supports the insertion of the 

 biceps ; the inner head springs from the inner side of the 

 head and neck of the tibia ; the middle head is confused at its 

 origin with the insertion of the accessory femoro-caudal. 

 This middle head appears to be wanting in Cypselus. It is 

 inserted by a strong tendon to the tarso-metatarsus, and 

 also, dividing, to the phalanges of the toes. 



Poplitei(s.~-This muscle passes between the tibia and 

 the fibula in most birds, but has been found to be sometimes 

 absent (e.g. Picus, &c.) 



TibiaMs Anticus. This muscle arises by two distinct 

 heads. The first is entirely tendinous, and is from the 

 external condyle of the femur. It forms a long and strong 

 ligament, which runs over the knee ; the second head is 

 fleshy, and is from the front part of the head of the tibia. 

 Its long tendon of insertion is attached to the metatarsal. 

 In certain birds (Chrysotis, Podargus, and owls) the tendon 

 and even a portion of the muscle are double. 



Extensor Digitorum Communis. This muscle arises gene- 

 rally from the front part of the tibia only, but sometimes its 

 fibres of origin stray on to the patella and on to the fibula. 

 The divisions of the tendon of the muscle are usually inserted 

 on to several phalanges of the toes, which they supply. It 

 is remarkable that the parrots are the only birds in which this 

 muscle supplies the hallux as well as the other toes ; it is, 

 therefore, in them, as GADOW remarks, truly an extensor 

 commutiis. In other birds digits I., III., IV. (when present) 

 are the only toes supplied. The common tendon divides in 

 various ways ; in Grus virgo the tendon divides into two, 



