PARTS BENEATH THE COMPLEXUS. 529 



The complexus is concealed by the splenius and trapezius. relations ; 

 Along the inner side is the semispinalis muscle, with the liga- 

 mentum nuchse. Beneath it are the small recti and obliqui 

 muscles, the semispinalis, and the posterior cervical nerves and 

 vessels ; and the cutaneous offsets of two or three of the nerves 

 perforate it. 



The complexus may be regarded as the cranial prolongation of use. 

 1he semispinalis muscle. 



Action. Both muscles will move the head directly backwards. Dissection 

 One will draw the occiput down and backwards towards its own side. n erv e s O f 



Dissection of vessels and nerves (fig. 192, p. 531). In the neck the neck; 

 the nerves and vessels will be brought into view by detaching the 

 complexus from the occipital bone and the spines of the vertebrae, 

 and carefully raising it from the subjacent parts. Beneath the 

 muscle are the ramifications of the cervical nerves, and the deep 

 cervical and other vessels, surrounded by dense connective tissue. 



Each nerve, except the first, divides into an inner and an outer inner and 

 branch. Dissect out first the inner branches, which lie partly over 

 and partly beneath the fibres of the semispinalis muscle (fig. 192,o). 

 The external branches are very small, and are given off between the outer 

 transverse processes close to where the trunks appear ; they are to branches ' 

 be looked for outside the complexus, entering the muscles prolonged 

 from the erector spinse and the splenius. 



The small first nerve is the most difficult of the set to find : it is first nerve 

 a short trunk, contained in the interval between the recti and 

 obliqui muscles near the head, and will be best found by looking 

 for the small twigs furnished by it to the muscles around. 



The deep cervical artery is met with on the semispinalis muscle; and the 

 a part of the vertebral artery will be found in contact with the first vessels: 

 nerve ; and the occipital artery will be visible crossing the occipital 

 bone. 



Opposite the thorax the dorsal nerves and vessels will be readily nerves and 

 displayed on the inner side of the longissimus dorsi muscle, on the Jhe^dorsal 

 removal of a little fatty tissue from between the transverse pro- region ; 

 cesses. External and internal branches are to be traced from each 

 nerve and vessel into the muscles : some of the former have been 

 seen in the interval between the ilio-costalis and the longissimus 

 dorsi. 



The two branches of the lumbar nerves and vessels are in the fc the lum- 

 same line as the dorsal ; but the inner set are difficult to find. 



The sacral nerves are placed beneath the multifidus spinse, and 

 will be dissected after the examination of that muscle. 



POSTERIOR PRIMARY BRANCHES OF THE SPINAL NERVES. The Posterior 



, -i .L i -11 i branches of 



spinal nerves, with a few exceptions in the cervical and sacral sp i n ai 



groups, divide in the intervertebral foramina into their anterior and nerves, 

 posterior primary branches. The posterior supply the integuments 

 and the muscles of the back, and are now to be learnt. 



IN THE NECK. The posterior primary divisions of the cervical In the neck 

 nerves are eight in number, and issue between the transverse pro- 

 cesses ; but those of the first and second, which begin on the neural 



D.A. M M 



