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



In Otaria the fibres have two directions. 



The Pterygoideus intemus (Lucae's pterygoideus and Humphry's pterygoid) in Phoca vitulina and 

 Arctocephalus is a strong muscle. It arises from the external surface of the pterygoid bone, and from 

 the fossa on the outer side of the hamular process in Arctocephalus only, for this is absent in Phoca. 

 It is inserted into the subcondyloid process of the lower jaw in Arctocephalus and in Phoca, beside 

 the inner side of the ramus below the condyle, to midway between it and the angle of the jaw. 

 The subcondyloid process is feeble in Phoca, but extensive in Arctocephalus. It is supplied by the 

 inferior maxillary nerve. 



In Otaria and Trichechus it has not been described. 



The Pterygoideus extemus in Phoca vitulina and Arctocephalus is a very small cylindrical bundle, 

 and arises in the former from below the foramen rotundum, and in the latter from the bridge 

 of bone connecting the alisphenoid with the external pterygoid plate over the foramen rotundum. 

 In both it crosses transversely outwards and is inserted into the inner side of the condyle of 

 the lower jaw. It is supplied by the inferior maxillary nerve. 



This muscle has not been described by Vrolik, Humphry, Lucae, nor by Murie. I found it in 

 all the specimens by dividing the symphysis and pulling the jaw gently outwards, when the bundle 

 of fibres attached as above was seen. 



The Muscles of the Neck. 



The only superficial muscle is the Stcrno-mastoid ; in Phoca vitulina it is a riband-shaped 

 muscle, and arises from the under surface and side of the anterior third of the presternum. It is 

 joined to its fellow for one inch and a half anterior to the presternum by a fine aponeurosis, 

 ascends to the mastoid process and is inserted into it at the root of the zygoma behind the insertion 

 of the trachelo-mastoid. It is supplied by external branches of the cervical plexus and a twig from 

 the spinal accessory nerve. 



In Arctocephalus it is triangular with the base resting on the fascial slip representing the 

 clavicle. It arises from the dorsal surface of the presternum and cartilage of the 1st rib, from the 

 deltoid ridge of the humerus between the insertions of the pectoralis major on the inner side and 

 the deltoid on the outer, blending with the origin of the inner part of the brachialis anticus below; 

 and from the fascial slip representing the clavicle. This last origin is thin, and midway between 

 the sternal and humeral origins is almost devoid of fibres, the deficiency being filled in with fibrous 

 tissue. The humeral part blends with the cephalo-humeral muscle along its outer edge and the 

 pectoral along its inner. The muscle runs forwards, narrows, and is inserted into the occipital ridge 

 near the external auditory meatus anterior to the splenius. It is supplied by twigs from the 

 external branches of the cervical plexus. 



In Otaria the sternal end of the muscle represented in Dr. Mime's Memoir (pi. lxxiii. fig. 33) is 

 like what I have described in Arctocephalus, and, as it extends outwards to the shoulder, it must have 

 other attachments than the manubrium, which is all that Murie gives in his description. 



In Trichechus it is as in Otaria, but a division into two parts is not described. 



The Infea-hyoid Region includes the sterno-thyro-hyoid and the thyro-hyoid. 



The Sterno-thyro-hyoid in Phoca vitulina is called the costo-thyreo-hyoideus by Lucae, the sterno- 



