86 STRUCTURE AND CLASSlFICATIOlSr OF BIRDS 



hinder part of the scapula and runs to the humerus, where 

 it is inserted on to the tuberculum mediale. 



Goraco-brachialis Externus. — This muscle, which is 

 relatively larger in the struthious birds, runs from the 

 coracoid to the beginning of the ' planum bicipitale ' of the 

 humerus, where it is generally covered by the tendon of the 

 biceps. It is noteworthy that among carinate birds this 

 muscle is largest in the tinamous, which thus approach the 

 ostrich tribe. It is most reduced in the Passeres, in some 

 of which, indeed, it has actually disappeared. 



Goraco-brachialis Internus. — Springs from the coracoid 

 and often from neighbouring parts of sternum. It is inserted 

 on to the median tubercle of the humerus. 



Pectoralis II. — This muscle arises from the ventral 

 surface of the sternum, from the coracoid, and from 

 the coraco-clavicular membrane. It is inserted by a long 

 tendon of attachment to the lateral tubercle of the humerus. 

 The muscle is small in ratites, large in carinates. 



Deltoides Major. — Arises from the acromion and the 

 dorsal part of the clavicle, and is inserted on to the deltoid 

 crest of the humerus. The muscle and the length of its 

 attachment vary much in size. It is large in Accipitres, 

 Passeres, &c., small in Aleae, Psittaoi, &c. It appears, indeed, 

 to be absent in Psittacula. 



Deltoides Minor. — This is a small muscle passing from, 

 the neighbourhood of the foramen triosseum. It is absent in 

 Phaethornis and (occasionally) in Cypselus. It is also 

 absent in Struthiones. 



Biceps. — This muscle consists typically of two heads, as 

 its name denotes. The longer of these arises from the 

 coracoid by a long tendon. The second head arises also 

 tendinously from the head of the humerus. The insertion 

 of the muscle is double, on to the radius and the ulna. The 

 division commences at a varying distance from the actual 

 insertion. 



In the penguins this muscle is totally absent. In 

 Colymbus, Pelecanoides, Thalassiarche, and other petrels, in 

 some AlcidsB, the coracoid head alone is present, the humeral 



