94 



limbs, everything is sacrificed to the swimming action of the arms, 

 which seem to be placed in the centre of elliptical masses of muscles 

 converging to a common centre, the fibres of which, by their successive 

 contraction, produce the monotonous circular motion requisite for swim- 

 ming ; while the feathering action of the hand is provided for by power- 

 ful supinators. In the posterior extremity the swimming action is more 

 like that of the tail of the fish, and consequently the feet are blended 

 with the tail, and their swimming action is effected chiefly by lowering 

 the insertions of all the muscles, thus sacrificing the delicate motions of 

 the thigh to the coarser action of the whole leg, considered rather as a 

 portion of the tail than as a distinct member of the body. 



Notwithstanding this subordination of the function of the muscles in 

 both extremities to the purposes of a single and simple action, it is 

 wonderful to observe how perfectly each muscle retains its indivi- 

 duality ; so much so, indeed, that there are few animals whose muscles 

 in both limbs are more perfectly developed than are those of the Seal. 



PAET I. HlJSCLES OE THE ANTERIOR LlMBS. 



1. M. pectoralis major, 10 oz. 



This muscle arises from the whole length of the sternum (14 

 inches), and is inserted into the well-marked pectoral ridge of 

 the humerus ; its fibres are succeeded at the xiphoid cartilage by 

 the converging fibres of the next muscle, which forms the lower 

 half of the superficial muscular ellipse, having its centre at the 

 head of the humerus. 



2. M. latissimus dorsi superficialis, 1 8 oz. 



Origin ; usual origin from posterior aspects of posterior ribs and 

 back, in front blending with the panniculus carnosus, it takes 

 an origin from the anterior line of the pelvis and mesian line of 

 the abdomen, completing its semielliptical origin at the xiphoid 

 cartilage, where it is succeeded by the great pectoral. 



Insertion ; by means of a tendon common to it and great pectoral 

 into pectoral ridge. 



3. M. Trapezius, . 4J oz. 



Origin ; from all the cervical and dorsal vertebrae. 



Insertion ; into the outer side of head of humerus, and into the 



spine of the scapula. 

 This muscle continues through another quadrant the elliptical 



circuit of muscles commenced by Eos. 1 and 2. 



4. M. humero-occipitalis, 4 oz. 



Origin ; from posterior line of the aponeurotic origin of the tempo- 

 ral muscle. 



Insertion ; pectoral ridge of humerus, inner side. 



This muscle is continuous with the trapezius behind, and with 

 the pectoralis major in front, and completes the elliptical circuit 

 of superficial muscles, Avhich may be regarded as an essential 

 characteristic of aquatic quadrupeds. It corresponds to the su- 



