130 ANATOMY OF UPPER EXTREMITY, ETC. 



ficialis cervicis, offsets from the subclavian artery. The 

 occipital artery, a branch of the external carotid (p. 45), 

 will also be seen emerging from beneath the tendons of the 

 sterno-mastoid, trachelo-mastoid, and splenius muscles, to 

 ramify upon the occipital bone; this artery sends off a 

 branch called the princeps cervicis, which passes down- 

 ward between the complexus and semi-spinalis colli mus- 

 cles, to inosculate with the profunda cervicis. 



The posterior branches of the sacral, lumbar, dorsal, and 

 cervical nerves, will also be observed ; they are mostly 

 small filaments accompanying the arteries, and supplying 

 the muscles and skin. The posterior branches of the first, 

 second, and third cervical nerves are however larger than 

 the others, and form a plexus upon the muscles of the 

 sub-occipital region, called the posterior cervical plexus. 

 The occipitalis major nerve, from the second cervical, is a 

 branch of considerable size, which passes upward, in com- 

 pany with the occipital artery, and ramifies between the 

 integument, which it supplies, and the posterior belly of 

 the occipito-frontalis muscle ; it sends numerous branches 

 to the muscles of the back of the neck. 



Under the title of ERECTOR SPIN^J are included a num- 

 ber of muscles of different length, extending from the 

 sacrum to the upper part of the neck ; small and pointed 

 over the sacrum, in the lumbar region the erector consti- 

 tutes a single, inseparable mass ; in thf dorsal region its 

 bulk gradually lessens, and in the neck it consists only of 

 slender prolongations. A strong and lustrous tendinous 

 expansion covers the sacral and lumbar portion ; and from 

 this, from the posterior surface of the sacrum, and from 

 the whole length of each transverse process of the lumbar 

 vertebrae, and the layer of the fascia lumborum external to 

 these, the erector spinse takes its origin. At the level of 

 the last rib, the muscle begins to separate into two por- 

 tions, the external being called the sacro-lumbalis, and the 

 internal the longissimus dorsi. 



The sacro-lumbalis muscle is inserted by separate tendons into the 

 angles of the six lower ribs ; here the muscle is reinforced by mus- 

 cular fasciculi arising from the upper margin of all the ribs, inter- 

 nally to th preceding insertions, and through them the sacro-luuibalis 

 is continued to the higher ribs, and to the transverse processes of three 

 or four lower cervical vertebrae. There is no separation between these 

 accessory fasciculi and the bulk of the sacro-lumbalis ; but those 

 derived from the six or eight lower ribs and inserted into the upper 

 ribs, are often described separately, as the musculus accessories ad 



