326 ELEMENTARY ANATOMY. [LESS. 



origin. Thus in many Birds it is the absolutely largest 

 muscle, and equals the weight of all the other muscles of 

 the body put together. In the last-named class it may send 

 a slip to the pollex, as in the Eagle (see Fig. 289, 2). 



Pectoralis minor. The smaller pectoral is a much less con- 

 stant muscle than the large one, being very frequently absent. 

 Even in animals closely allied to man (e.g. many Apes) it is 

 inserted into the capsular ligament of the humerus instead of 

 into the coracoid process. It may form one with the pecto- 

 ralis major, as in Birds. 



The sub-clavius is also an inconstant muscle. It may take 

 on an enormous development and be singularly modified, as in 

 Birds, where it arises beneath the pectoralis, and is so inserted 

 as by its action to antagonize that muscle ; for it sends a 

 tendon between the clavicle and coracoid, and the scapula 

 (the margin of the interspace through which it passes serving 

 as a pulley), by which the direction of its force is changed, 

 so that it serves to elevate instead of to depress the humerus. 



Serratus mag nits. This, which really is one muscle with the 

 levator anguli scapulae, may be much more extensive or much 

 more restricted than in the human subject. In Quadrupeds 

 (e.g. the Horse) the serrati of the two sides serve to sling the 

 trunk from the scapulae, or summits of the columnar fore- 

 limbs. It may consist of several detached parts, as in the 

 Chameleon, or be exceedingly small, as in Menopoma 

 (Fig. 283). 



The deltoid is a nearly constant muscle in Vertebrates above 

 Fishes, but may be very small, as in the Horse, or very large, 

 as in the Bat, or it may be divided into several parts. 



The supra-spinatus of man is normal as compared with 

 that of other animals of his class ; but, by a strange excep- 

 tion, it may be placed only on the inner (or body) side of 

 the scapula, as in the Echidna. 



The infra-spinatus\ which is also normal in man, may (as 

 in the Echidna) be placed at the most anterior part of the 

 outer surface of the scapula. 



The teres minor may coalesce with the last-noticed muscle, 

 as in the Two-toed Ant-eater. The minor may be larger 

 than the major, as in the Horse. 



The teres major is normal in man, but it may attain a 

 very much greater relative size, as in the Mole. 



The subscapularis is generally in Mammals much as it is in 

 the human subject. It may be considerably smaller, however 

 (as in Cetaceans) ; and by a singular exception it may (as in the 



