152 THE VOYAGE OF H.M.S. CHALLENGER. 



bundle near the posterior angle of the scapula ; this is partly tendinous on its outer side, and is 

 inserted into the vertebral border of the cartilaginous plate at the posterior angle, posterior to the 

 insertion of the rhomboideus dorsi, which sends a few fibres to it. The five cervical slips and the 

 five anterior thoracic are inserted into the inner lip of the vertebral border, from 1 inch posterior 

 to the anterior angle of the scapula to the posterior angle, and into the ventral side of the cartila- 

 ginous plate, with the exception of a- small piece which is for the insertion of the rhomboideus dorsi, 

 and joins with the insertion into the posterior angle. The cervical digitations are distinct, while 

 those from the anterior thoracic region are not quite so, but touch each other from their origin to 

 their insertion. The posterior slip interdigitates with the latissimus dorsi, the five anterior to this 

 one with the external oblique. 



The origins of the serratus in the Phocinas and in Arctocephalus differ in the number of 

 the digitations from the trunk; in the latter there are two more coming from the 10th and 11th 

 ribs. In the Phocinas it only interdigitates with the external oblique, whereas in Arctocephcdus it 

 interdigitates with it and the latissimus dorsi. 



By the greater size of the cartilaginous plate in the Phocinas a change in the two insertions is 

 brought about. The plate in Arctocephalus is only a narrow bar, but in the Phocinas it is very wide. 

 In the Phocinas the cervical slips fix themselves upon the anterior vertebral border of the bone 

 and anterior end of the cartilaginous bar ; the anterior thoracic slips follow the junction of the bar 

 with the bone from the termination of the cervical slips to the posterior angle, and the posterior 

 thoracic begin where the last ended, and follow the vertebral border of the plate to its anterior end. 

 By this arrangement a circle of fibres surrounds the cartilage, and a clear space is left in the centre. 

 The rhomboidei cervicis, capitis, and dorsi are fixed to it in this order from before backwards. 

 In Arctocephalus the cervical and the anterior thoracic are attached to the scapula and ventral 

 surface of this plate as far as the posterior angle, leaving uncovered a small part of the vertebral 

 border of the plate near the posterior angle for the rhomboideus dorsi. The posterior thoracic slips 

 go to the posterior angle. In Otaria it arises from ten ribs, and in Trichechus from eight. 



The digitations of the cervical serratus are in a plane with the digitations of the levator anguli 

 scapulas, and are so combined in many Mammals that one muscle is the result. The slips are not so 

 closely approximated in the Phocinas and Arctocephalus as to prevent a natural division. Professor 

 Humphry states that it forms a continuous sheet with the levator, and Dr. Murie says in Otaria " that 

 the serratus digitations were tolerably fused together, so that they formed but one continuous sheet." 

 In Otaria he makes special reference to its " two upper nuchal slips which are inserted quite on the 

 dorsal surface of the scapula," and in the Trichechus explains that " the highest, as in Otaria, is 

 more or less separate, and is inserted into the dorsum of the scapula between the angle and spine 

 on the vertebral border." When the levator anguli scapulas is not well developed and is absorbed 

 by the serratus, and the fusion has not been absolute, then the serratus must be scrutinised 

 closely to discover what has become of it. The difference in its anterior part in Otaria and 

 Trichechus by the outer slips going to the dorsum of the scapula, and the want of perfect fusion of 

 the slips, makes it doubtful as to the highest being serratus. The atlanto-scapular in Arctocephalus 

 is the levator anguli scapulas of Dr. Murie in the Otaria and Trichechus. To justify this observa- 

 tion, the myological researches of the various investigators on the Phocinas in which there is no 

 atlanto-scapular must be quoted. Professor Humphry describes a levator anguli scapulas inserted 

 into the base of the scapula. Professor Lucae in the same animal gives, in one of his plates, a 



