MUSCULAR SYSTEM 605 



B. Muscles supplied by cranial nerves, 

 a. Muscles of the Visceral Skeleton, 



1. Muscles of the Jaws. 



2. Muscles of the Hyoid apparatus (page 452). 

 /?. Muscles of the Syrinx. 



•y. Muscles of the Ear (page 178) and Eye (page 229). 



A. The Muscles of the Stem {A.a) and of the Extrem- 

 ities {A.^) not only exhibit many varieties in different Birds, but 

 they are also very numerous, about one hundred pairs being recog- 

 nized. To describe them all adequately would go far beyond the 

 scope of this Avork, while simply to name them and devote a few lines 

 to the general condition of each would, considering their great vari- 

 ability, be of no practical use, for the dissection and recognition of 

 Muscles is not easy. In what follows, therefore, only some of 

 those Avill be dealt with which, rightly or wrongly, bear the 

 reputation of being of taxonomic value. 



Musculus pedoralis, consisting of a thoracic, propatagial and 

 abdominal portion — the first forming the chief muscular mass of 

 the breast and arising from the sternum in the shape of a U — the 

 two arms of which surround the m. sup'acoracoideus, the longer 

 formed by the clavicle, sterno-clavicular membrane and the side 

 of the keel, the shorter by the body and lateral margin and 

 membranes, filling the sternal notches, and adjoining parts of the 

 sternal ribs. All the fibres of this great muscle, which occupies 

 most of the ventral surface of the sternum, converge toward the 

 shoulder into one or two tendons, the principal of which is inserted 

 on the greater tubercle and the upper crest of the humerus, and 

 the muscle is the chief depressor of the upper arm during the 

 down stroke, Avhile it also rotates it forwards. This last is especially 

 its effect in the Spheniscidse, giving their wings the screw- like 

 motion, and is in conformity with the peculiar fact that the tendon 

 of the clavicular portion of the muscle is attached to the Avhole 

 length of the radial sm'faee of the humerus betAveen its inferior 

 crest and the head. The Aveight of both the pectoral muscles 

 together is said to amount to about 1/14 in Birds-of-Prey and 1/11 

 in Wild Geese of that of the Avhole body. 



31. swpracm'acoideus, arising chiefly from the sides of the angle 

 formed by the keel and body of the sternum, and from part of the 

 coraco- clavicular membrane, and covered by the m. pedoralis, 

 ascending from the sternum along the inner and anterior surface 

 of the coracoid, passing by a strong tendon through the foramen 

 triosseum and the region over the joint, and inserted on the upper 

 tubercle of the crest of the humerus, which it rotates and ab- 

 ducts. This muscle is generally described as a second pectoral or 

 as the m. suhdavms ; but Alix and Fiirbringer have shewn that its 



