64 PEOCEEDINGS OF THE NATION" AL MUSEUM vol.73 



representing a longissimus cervicis. Mediad, and craniad of the 

 fourth thoracic vertebra, the biventer cervicis intervened, and adjoin- 

 ing the spines was the spinalis dorsi, distinguishable with clarity 

 craniad of the eighth rib. The spinalis cervicis portion of this 

 inserted upon the cervical spines to and including the axis. 



In the Phoca this was an astonishing mass of muscle, the two sides 

 together measuring 210 mm. in width, and a definite impression was 

 gained that although enormously stronger than in the eared seal 

 dissected, its normal uses were for less complicated and more re- 

 stricted in movements. Caudad it was clearly divisible into a medial 

 longissimus dorsi and an iliocostalis lumborum of slightly lesser 

 width. These two, however, were not separable with any degree 

 of east throughout their deeper portions. The superficial fibers of 

 the iliocostal part were seen to arise from the glistening aponeurosis 

 covering the longissimus, but the chief origin was fleshy and from 

 almost the entire cranially-directed surface of the " medial " border 

 of the ilium, forming an attachment of enormous strength. Within 

 50 mm. of this bone the iliocostal had attained a width of 40 and a 

 depth of 45 mm. More craniad there was fibrous connection with 

 the ribs over which it passed until a tendinous slip was given off to 

 join the seventh, but apparently no other ribs in that vicinity. The 

 muscle then broadened and developed tendon bundles, five of these 

 passing cranio-dorsad to join the transverse processes of the first five 

 thocacic vertebrae and four others cranio-ventrad to join the first 

 four ribs. Thus, the anterior part of this muscle was simple, doing 

 little but acting as an anchor for the posterior part. In the pos- 

 terior thoracic region the longissimus had rather obscure spinalis 

 dorsi elements, there being tendons extending cranio-mediad to join 

 each spine, but no distinct muscle could be separated. In its more 

 lateral part the longissimus had slight fibrous attachment to the ribs 

 and mediad there were tendons gradually developing from the trans- 

 verse processes extending craniad to be lost in the muscle mass. 

 These increased in size in cranial sequence from the last thoracic and 

 the series culminated in a very strong tendon from the tenth after 

 which these ceased. Thus, these tendons seemed to be largely instru- 

 mental in the development, upon these thoracic vertebrae only, of 

 distinct metapophyses and constituted a semispinalis dorsi element. 

 There were also smaller longissimus tendons of opposite inclination 

 attached to the anapophysis of each vertebra. At about the seventh 

 thoracic the longissimus split into two parts, both rapidly becoming 

 slender. The more medial was the spinalis dorsi, becoming the 

 spinalis cervicis. Its attachments were by fasciculi to the spines as 

 far as the fourth cervical, although a few fibers may have extended 

 still farther craniad. The more lateral division was the longissimus 



