58 PROCEEDINGS OF THE XATIOXAL MUSEUM vol.73 



LUMBAR MUSCLES 



M. quadrattts lambomm (figs. 11, 24) in the ZalopTms arose by slender 

 bundles from the last three thoracic and all the lumbar vertebrae. 

 The bundle coming chiefly from the anterior centrum of the penulti- 

 mate lumbar extended upon the left side of the base of the femoral 

 process of the ilium and its fibers fused with those of the iliacus. 

 Upon the right side this slip of the quadratus inserted fully 2 centi- 

 meters farther craniad and was much more slender. In the Phoca 

 origin did not extend craniad of the penultimate thoracic vertebra 

 and I could not demonstrate that any of its fibers reached the ilium, 

 T3ut only the sacrum. The whole muscle was very much more robust 

 than in the otariid. 



MUSCLES OF THE BACK 



Superficial, secondary back muscles. — M. cephalohumeral (figs. 

 2, 3, 9, 16, 17, 18, 19) should perhaps be placed here. It is formed by 

 the fusion of the clavotrapezius and clavobrachialis as in many 

 carnivores lacking a clavicle. In the Zalophus it was rather complex 

 and arose by three, heads — a narrow one from the connective tissue 

 just laterad to the tip of the presternum; next a second narrow one 

 from the cranial margin of the deep pectoral, and third a broad 

 head that extended rostrad from the fascia above the entire deltoid 

 ridge of the humerus. The three heads joined and the broad, rather 

 thin sheet of muscle resulting inserted along the medial two-thirds 

 of the occipital crest and thence from the middorsal line as far as the 

 hunierotrapezius. Its chief action is probably in certain move- 

 ments of the head, but in the Phoca this was reversed, and it operates 

 rather to move the forearm. In this animal it arose as a tenuous 

 sheet from the middorsal line as far rostrad as the interorbital con- 

 striction and caudad beyond the occiput. The fibers passed ventro- 

 caudad over the side of the neck and converged to insert upon the 

 lesser tuberosity and the adjoining portion of the greater as well. 

 Miller stated that in Arctocephalus the more caudal attachment was 

 to the humerus only. The condition of this muscle in his Phoca was 

 the same as in mine, save that insertion was chiefly upon the greater 

 tuberosity. In Odohenus caudal attachment was to the humerus 

 only, but as near as I can tell the condition in Ewmetopias was more 

 comparable with that of Zalophus. 



M. humerotrapezius (figs. 3, 7, 9, 16, 17) is homologous with the usual 

 acromiotrapezius. In the Zalophus it arose from the middorsum ad- 

 joining and in the same plane with the cephalohumeral, the origin 

 extending caudad over a part of the spinotrapezius. The fibers were 

 directed latero-ventrad and it was free from the underlying spine of 

 the scapula along the dorsal two thirds of the latter, but to the ven- 



