AET. 15 AXATOMY OF THE EAEED AND EARLESS SEALS HOWELL 63 



sad of the spine. Not mentioned by Murie as a distinct muscle in 

 Eumetopias but possibly included as a part of his serratus magnus. 



M. atlantoscapularis inferior (figs. 7, 9, 16, 17, 19) also arises from the 

 transverse process of the atlas, but superficial to the origin of the 

 superior division. In the ZalopJws insertion was by fascia upon the 

 ventral two-fifths of the spine of the scapula adjacent to the anterior 

 rhomboid and upon the neighboring part of the humerus. In the 

 Phoca the insertion had migrated more distad and was by fascia 

 upon the greater tuberosity and deltoid ridge of the humerus ad- 

 joining (ventrad of) the humerotrapezius. Miller called this muscle 

 atlantohumeral in Phoca and atlantoscapular in Arctocephalus^ ac- 

 cording to the insertion. They are undoubtedly homologous and I 

 prefer to employ the same term for both, even though it is slightly 

 ambiguous in the case of the seal. It is the levator anguli scapulae 

 of Murie. In addition the latter mentions, rather vaguely, an acces- 

 sor}^ slip in Odobenus which he considers to be the homologue of a 

 levator claviculae. 



M. serratus posticus. Deep to the rhomboid layer of the Zcdophus 

 and a couple of centimeters caudad to any part of the scapula was 

 a tenuous, vestigeal bit of muscle which arose from fascia and ended 

 likewise beneath the caudal border of the larger rhomboid. I did 

 not distinguish it in my Phoca, possibly because of the presence 

 of clotted blood in this region, but Miller did in his. It has not been 

 reported from any of the other eared seals proper, but Murie found it 

 fairly well developed in Odobenus. 



Deep, intrinsic back muscles. — M, splenius (figs. 2, 5, 16, 17) 

 arose from the middorsum, extending in the Zalophus from the 

 occiput to about the second thoracic spine, and inserting along the 

 entire occipital crest, from the vertex to the mastoid process, at the 

 latter point being continuous with the trachelomastoid. In the Phoca 

 origin extended craniad only as far as the spine of the axis, and 

 insertion was limited to the mastoid process. This is Murie's splenius 

 capitis. 



M. erector spinae, sacrospinalis, extensor dorsi communis or long 

 system of the back was but moderately developed in the Zalophus^ and 

 the pair of muscles together in the specimen dissected measured but 

 100 mm. in width at the widest part in the posterior thoracic region. 

 It was indivisible in the lumbar region, the whole muscle arising 

 from the vertebrae, sacrum, and inner surface of the ilium. Be- 

 tween the ninth and sixth ribs it was partly separable into an 

 iliocostalis dorsi and longissimus portion, but craniad to the sixth 

 rib these once more to all intents constitute a single muscle. This 

 fused part sent a slip to each of the first 10 ribs and to the anapo- 

 physes of each of the last five cervical vertebrae, this part at least 



