REPORT ON THE SEALS. 227 



of the interparietal bone. A small fasciculus is continuous with the rhomboideus cervicis. The 

 ill ires course outwards and forwards, and are inserted partly by muscular fibres and partly by 

 aponeurosis into the occipital ridge. It is supplied by the external division of the great occipital 

 nerve, by a branch of the external division of the 3rd cervical, and by a branch from the suboccipital. 



In Arctocephahis it has the same shape and relations as in Phocn vitulina, and arises from the 

 ligamentum nucha?, the 7th cervical vertebra, and the three anterior dorsal spines, and is inserted into 

 the occipital ridge from the posterior termination of the sagittal suture, to the posterior margin 

 of the external auditory meatus. It is blended with the trachelo-mastoid near its insertion. In 

 Otaria and Trichechus a splenius capitis and colli are described. The former is the same as the 

 splenius in Arctocephahis, and the splenius colli is the trachelo-mastoid in Arcloccphalus. 



The Erector spinm in Phoca vitulina divides into the sacro-lumbalis, longissimus dorsi, trans- 

 versalis colli, and trachelo-mastoid. In Arctocephahis, in addition to the above, the spinalis dorsi 

 and colli are found. 



In Phoca vitulina it lies between the caudal region and the last rib. Its aponeurosis extends 

 from the sacral to the dorsal region as far as the 14th dorsal spine, crosses over the multifidus, 

 forming its dorsal covering, and ends laterally on the middle of the dorsum of the erector spinas 

 posterior to the last rib. It is a massive roll of muscle anterior to the ilium, but posterior to this 

 is in two small but distinct parts, corresponding to the sacro-lumbalis and the longissimus dorsi. 

 Anterior to the ilium there is an indication of the existence of two muscles, for a partial fibrous 

 partition is found running for a short distance into the fibres from the anterior dorsal surface of the 

 sacrum. The erector arises in two parts, the division ultimately forming the longissimus dorsi from 

 the rudimentary zygapophyses of the 3rd, 4th, 5th, and 6th caudal vertebras, from the transverse 

 process of the 1st caudal, from the ligamentous structures covering the dorsum of the sacrum 

 between the zygapophyses and the transverse processes, and from the ligamentous partition on each 

 side. It runs forward as the erector spins, lying next the zygapophyses of the lumbar vertebra?, 

 and turns over the last rib. The division joining the fibres of the erector, and forming the 

 sacro-lumbalis, arises from the transverse processes of the 1st, 2nd, and 3rd caudal vertebras, and 

 from the zygapophyses of the 1st and 2nd caudal vertebra?. This origin is bound to the outer side 

 of the posterior sacro-iliac ligament, and runs into the erector anterior to the ilium, forming the 

 partial septum already mentioned. This structure is supplemented by a tendon from the dorsal 

 surface of the ilium, and by fibres from its anterior surface, from the same surface of the sacrum, and 

 from the ligament between them, the three last origins being ventral to the septum. The 

 longissimus portion of the erector from the caudal region is inserted into the dorsal posterior borders 

 of the anterior zygapophyses of the 2nd, 3rd, 4th, and 5th lumbar vertebras, into the anapophyses of 

 the last dorsal and 1st lumbar vertebra', into the outer surface of the lumbar vertebras, by muscular 

 fibres extending from the dorsal tips of the anterior zygapophyses to midway between these and the 

 tranverse processes, and into the inner posterior third of the last rib. The sacro-lumbalis portion 

 is inserted into the ventral halves of the outer surfaces of the lumbar vertebras, into the outer sur- 

 faces of their transverse processes, and into the outer two-thirds of the posterior border of the last 

 rib to within 1 inch from its outer end. The erector is under cover of the lumbar fascia. 



In Arctocephahis the longissimus dorsi is not separable from the sacro-lumbalis as in Phoca, 

 yet the formation of the two is partly evident in the lumbar region. The erector arises in the 

 sacral region by an aponeurosis, from the spines of some of the caudal and all the sacral vertebrae, 



