THE DISSECTION OF THE BACK 63 



Musculus Splenius. The splenius has a continuous origin 

 from the lower half of the ligamentum nuchae, and from the 

 spines .of the seventh cervical and upper six thoracic vertebrae. 

 Its fibres pass obliquely upwards and laterally, forming a thick 

 flat muscle, which soon divides into a cervical and a cranial 

 portion, termed respectively the splenius cervicis and the 

 splenius capitis. 



The splenius cervicis turns forwards and is inserted, by 

 tendinous slips, into the posterior tubercles of the transverse 

 processes of the upper two or three cervical vertebrae, medial 

 to the levator scapulae. 



The splenius capitis passes under cover of the upper part 

 of the sterno-mastoid muscle, and gains insertion into the 

 lower part of the mastoid portion of the temporal bone and 

 into the lateral portion of the superior nuchal line of the 

 occipital bone. To see the insertion, the sterno-mastoid 

 muscle may be divided along the superior nuchal line, but 

 it must not be detached from the temporal bone. The 

 splenius capitis and cervicis bend the head and neck respec- 

 tively backwards and turn them to the side on which the 

 muscles lie. The splenius capitis and splenius cervicis are 

 supplied by the posterior rami of the cervical nerves. 



Dissection. The deeper spinal muscles must now be dissected. 

 Begin by reflecting the splenius muscle. Detach it from its 

 origin and throw it laterally and upwards towards its insertion. 

 Whilst doing that preserve the cutaneous branches of the cervical 

 nerves which pierce the muscle. 



When the splenius capitis is fully reflected, a small triangular 

 space will be noticed close to the superior nuchal line of the 

 occipital bone. Anteriorly, it is bounded by the longissimus 

 capitis (O.T. trachelo-mastoid) ; posteriorly, by the lateral 

 border of the semispinalis capitis (O.T. complexus) ; and above, 

 by the superior nuchal line of the occipital bone. The floor of 

 the little space is formed by the superior oblique muscle of the 

 head, and it is traversed by the occipital artery, which in that 

 part of its course gives off its descending branch (O.T. arteria 

 princeps cervicis), and its meningeal branch. 



The Third Layer of Muscles. Under this head are included a series 

 of muscular strands which stretch, with a greater or less degree of continuity, 

 along the entire length of the dorsal aspect of the vertebral column. In the 

 lumbar region they constitute a bulky fleshy mass which may be considered 

 the main starting-point. The mass is the muscuhis sacro-spinalis, which 

 has the following origins : (i) from the spines of all the lumbar vertebrae ; 



(2) from the supraspinous ligaments which bind the lumbar spines together ; 



(3) from the dorsum of the sacrum and from the posterior sacro-iliac liga- 

 ment ; (4) from the posterior fifth of the iliac crest ; (5) from the deep 

 surface of the posterior layer of the lumbo-dorsal fascia. In great part the 



