MUSCULAR SYSTEM 605 
B. Muscles supplied by cranial nerves. 
a. Muscles of the Visceral Skeleton. 
1. Muscles of the Jaws. 
2. Muscles of the Hyoip apparatus (page 452), 
B. Muscles of the Syrmx. 
y. Muscles of the Ear (page 178) and Eyx (page 229). 
A. The Muscles of the Stem (4.a) and of the Extrem- 
ities (4.8) 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 work, 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 will be dealt with which, rightly or wrongly, bear the 
reputation of being of taxonomic value. 
Musculus pectoralis, 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. supracoracoideus, 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, while it also rotates it forwards. This last is especially 
its effect in the Spheniscidx, 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 whole 
length of the radial surface of the humerus between its inferior 
crest and the head. The weight 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 whole body. 
M. supracoracoideus, 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. pectoralis, 
ascending from the sternum along the inner and anterior surface 
of the coracoid, passing by a strong tendon through the foramen 
triossewm 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. subclavius ; but Alix and Fiirbringer have shewn that its 
