MUSCLES OF THE BACK. 177 



arises from the lower half of the ligamentum nuchse, from the 

 spinous process of the last cervical vertebra, and from the spinous 

 processes of the. six upper dorsal* and supra-spinous ligament; it 

 divides as it ascends the neck into the splenius capitis and colli. 

 The splenius capitis is inserted into the rough surface of the occi- 

 pital bone between the two semicircular ridges, and into the mas- 

 toid portion of the temporal bone. 



The splenius colli is inserted into the posterior tubercles of the 

 transverse processes of the three or four upper cervical vertebrae. 



Relations. By its superficial surface with the trapezius, sterno- 

 mastoid, levator anguli scapula?, rhomboideus minor and major, 

 and serratus posticus superior. By its deep surface with the 

 spinalis dorsi, longissimus dorsi, semi-spinalis colli, complexus, 

 trachelo-mastoid, and transversalis colli. The tendons of insertion 

 of the splenius colli are interposed between the insertions of the 

 levator anguli scapulas in front, and the transversalis colli behind. 



The splenii of opposite sides of the neck leave between them a 

 triangular interval, in which the complexus is seen. 



Fourth Layer. 



Dissection. The two serrati and two splenii must be removed 

 by cutting them away from their origins and insertions, to bring 

 the fourth layer into view. 



Three of these muscles, viz. sacro-lumbalis, longissimus dorsi, 

 and spinalis dorsi, are associated under the name of erector spins. 

 They occupy the lumbar and dorsal portion of the back. The 

 remaining four are situated in the cervical region. 



The sacro-lumbalis and longissimus dorsi arise by a common 

 origin from the posterior third of the crest of the ilium, from the 

 posterior surface of the sacrum, and from the lumbar vertebrae: 

 opposite the last rib a line of separation begins to be perceptible 

 between the two muscles. The sacro-lumbalis is inserted by sepa- 

 rate tendons into the angles of the six lower ribs. On turning the 

 muscle a little outwards, a number of tendinous slips will be seen 

 taking their orgin from the ribs, and terminating in a muscular 

 fasciculus, by which the sacro-lumbalis is prolonged to the upper 

 part of the thorax. This is the musculus accessorius ad sacro-lum- 

 balem : it arises from the angles of the six lower ribs, and is 

 inserted by separate tendons into the angles of the six upper ribs. 



The longissimus dorsi is inserted into all the ribs, between their 

 tubercles and angles.f 



The spinalis dorsi arises from the spinous processes of the two 

 upper lumbar and two lower dorsal vertebrae, and is inserted into 

 the spinous processes of all the upper dorsal vertebrae; the two 

 muscles form an ellipse, which appears to enclose the spinous pro- 

 cesses of all the dorsal vertebra?. 



* Homer makes it to arise but from four dorsal vertebra;. G. 



t It is also inserted into the ends of the transverse processes of all the dorsal verte- 

 bra;. G. 



23 



