REPORT ON THE SEALS. 153 



levator with a similar insertion, and in my dissections of the Phocinae and Arctoccpludus I find in all 

 a levator which corresponds to the nuchal slips called serratus in Otaria and Trichechus, so that I 

 regard the nuchal slips as the levator in the Otaria and Trichechus. 



It pulls the scapula away from the spinal column, the posterior fibres rotate it outwards, and 

 the anterior fibres from the neck must pull the shoulder forwards. 



The Muscles of the Shoulder. — In the Phocinaj are found the deltoid, subscapulars, sub- 

 scapulo-capsularis, supraspinatus, infraspinatus, teres minor, and teres major. 



In Arctoccpludus the teres minor and subscapulo-capsularis are absent, but this animal possesses 

 in addition an episubscapularis. 



The Deltoid is placed upon the infraspinatus behind the scapular spine. It is in the 

 form of a quadrant, and arises from the entire posterior border of the spine of the scapula, 

 above the spinal origin of the infraspinatus ; from the dense fascia between the outer termina- 

 tion of the spine and the shoulder-joint ; slightly from the dorsal surface of the capsule of the 

 shoulder-joint ; from the scapula internal to the vertebral end of the spine and internal to the 

 origin of the infraspinatus ; from the dorsum of the cartilaginous plate to a small extent ; and 

 from a narrow surface between the infraspinatus and the dorsi-epitrochlear muscles. The fibres 

 course towards the humerus, overlap part of the triceps, and cross the upper half of its dorsal 

 surface ; from the middle to the axillary end of the spine it receives some of the fibres of the 

 anterior part of the trapezius, then passes over the shoulder-joint where the atlanto-humeral partly 

 joins it along its anterior border. It is inserted into the lower half of the outer edge of the great 

 humeral tuberosity (deltoid ridge). 



In Arctoccpludus gazclla it lies posterior to the scapular spine, and is almost rectangular. It 

 arises from the whole extent of the posterior lip of the spine, from the posterior border of it, from 

 the capsule of the shoulder-joint dorsally, from the scapula by tendinous fibres between the spine 

 and the vertebral border, from the vertebral border by muscular fibres, from the dorsum of the 

 cartilaginous plate alongside of the vertebral border, and from the adjacent sides of both to the 

 posterior angle. All the fibres incline to the outer surface of the humerus, a few to the outer end 

 of the spine blend with a small group of the atlanto-scapular. It is inserted into the outer rim of 

 the deltoid ridge, and into the dorsal part of the capsule of the shoulder-joint. The under two- 

 thirds of the insertion is tendinous. From the corner of the muscle joining the lowest part of the 

 deltoid ridge, a tendinous slip goes to the fibro-cellular bar lying upon the anterior border of the 

 radius. 



A glance at the scapulre of the Phochue and Arctoccphalus impresses one with their dissimilarity 

 of mould. The spine, which is the boundary line between the supra- and infraspinous fossae, is 

 situated at the junction of the anterior third and the posterior two-thirds of the dorsum in the 

 Phocinaj. In Arctoccpludus it is at the junction of the anterior two-thirds and the posterior 

 third (PI. VII. fig. 2). The osteological differences between these two bones show clearly the 

 variety in form, function, and development of the soft structures which are attached to them, and 

 point to the likelihood of some muscles being present in the one and not in the other, which is the 

 case. The form and position of the origin of the deltoid in the Phocinse and Arctoccpluilus are 

 markedly unlike. In the former it approaches the shape of a gun, with the stock at an acute angle 

 to the barrel, in the latter it is like an old-fashioned scythe.' The barrel of the gun and the handle 



(ZOOL. CHALL. EXP. — PART LXVIII. 18S8.) Yyy 20 



