REPORT ON THE SEALS. 151 



cellular tissue, I could not be positive as to a natural division. However, as the presternal fibres 

 in the Phocinte and Arctocephcdus are the only ones of the pectoral muscle which are not inserted 

 into the humerus and forearm, but end among the fibres of the sternal part in the Phocinte, and 

 of the sterno-cleido-mastoid and sternal part in Arctocephalus, it shows how closely these prajsternal 

 parts are allied. 



In Otaria the second division (i.e., the thoracico-abdominal) is inserted partly by fascia, which 

 joins the aponeurotic fascia of the forearm. In Arctocephalus there is no fascia going to that of the 

 forearm. 



In Trichechus the second division, deep layer or pectoralis minor (i.e., the thoracico-abdominal 

 part), is inserted directly into the whole length of the shaft of the humerus, so there is no blending 

 of the second part with the first as in Arctocephalus and Otaria. 



Neither in the Phocinse nor in Arctocephalus have I made out the third and smallest division 

 (sterno-scapidar) described in Otaria and Trichechus, and Professors Vrolik, Humphry, and Lucae 

 do not mention such a muscle in their researches on Phoca. 



Dr. Murie inclines to the view that the two most superficial layers in Otaria are a divided 

 pectoralis major, and not the minor ; the third layer he classes as the sterno-scapular. In de- 

 scribing his Trichechus, he uses the names first layer or pectoralis major, second layer or 

 pectoralis minor, and third layer. Although the name pectoralis minor is used by Murie, I do 

 not think this muscle really exists in the Phocinse and other Seals, for as the insertion acts as a 

 guide in determining the identity of a muscle, and as there is a well-marked lesser tuberosity in the 

 humeri of the Phocinse, and a better representative of it in the Arctoccphcdi, still no fibres of the 

 pectoral muscle find their way to it, but all pass over to the deltoid ridge. If the pectoralis minor 

 did exist, the insertion' would be into the lesser tuberosity of the humerus, because the coracoid is 

 inside the shoulder-joint in the seals. 



The Lateral Thoracic Region contains the Serraius macjnus, which covers the trunk and the 

 neck. This muscle arises by five muscular slips from the ventral transverse processes of the five 

 posterior cervical vertebras behind the scalenus anticus, from the outer and posterior surfaces of the 

 nine anterior ribs at the junction of the bones with their cartilages. The five lowest interdigitate 

 with the external oblique ; the slips from the first and second ribs are not divisible near their origin. 

 From the insertion into the base of the scapula it is seen that the muscle is fixed in three 

 ways. The five cervical slips are inserted into the vertebral border of the scapula, between the 

 anterior angle and the cartilaginous plate, to 1 inch posterior to its anterior end. The four 

 anterior thoracic digitations crossing from the trunk are inserted obliquely across the ventral 

 surface of the cartilaginous plate between the cervical part ending 1 inch posterior to the anterior 

 end of the cartilaginous plate, and the osseous posterior angle of the scapula. The five posterior 

 ascending from the trunk are inserted into the vertebral border of the cartilaginous plate, and 

 slightly into the ventral surface of it, extending as far forward as 1 inch posterior to the spine. 

 These five digitations are attached in the opposite order of origin ; the 5th goes into the posterior 

 angle, the 6th is placed anterior to it on the scapula, and the 9th is the highest. In the large 

 Phoca vitulina there were ten digitations from the trunk. 



In Arctocephcdus gazella it arises by sixteen digitations, almost as in Phoca vitulina. The fibres 

 course to the base of the scapula. The six posterior digitations from the trunk form a strong 



