THE DISSECTION OF THE BACK 173 



each side of the back of the neck. It represents a powerful 

 elastic structure in quadrupeds, which helps to sustain the weight 

 of the dependent head. In man, however, there is not much 

 elastic tissue developed in connection with it, and it appears 

 to be a continuation upwards of the supraspinous ligament 

 from the spine of the seventh cervical vertebra to the external 

 occipital protuberance. In shape it is somewhat triangular. 

 By its base it is attached to the external occipital crest ; by 

 its anterior border it is fixed by a series of slips to the 

 posterior tubercle of the atlas, and to the bifid spines of the 

 cervical vertebras, in the intervals between their tubercles. Its 

 apex is attached to the spine of the seventh cervical vertebra, 

 whilst its posterior border is, in a measure, free, and gives 

 origin to the trapezius, rhomboid, serratus posterior superior, 

 and splenius muscles. 



Arteria Profunda Cervicis. The deep cervical artery springs 

 from the costo-cervical branch of the subclavian, and reaches 

 the dorsum by passing posteriorly between the transverse 

 process of the last cervical vertebra and the neck of the first 

 rib. At the present stage of the dissection it is seen ascend- 

 ing upon the semispinalis cervicis muscle and anastomosing 

 with the descending branch of the occipital. Both vessels 

 anastomose with twigs from the vertebral artery. 



The arteria profunda cervicis is accompanied by a large 

 vein the vena profunda cervicis. This vessel begins in the 

 sub-occipital plexus, and it ends in the vertebral vein close to 

 its termination. It reaches this point by turning forwards 

 under the transverse process of the last cervical vertebra. 



Posterior Branches of the Spinal Nerves. The nerves of 

 the back must now be examined. They are the posterior 

 branches of the spinal nerves. With four exceptions (viz., 

 the first cervical, fourth and fifth sacral, and the coccygeal 

 nerves), each posterior division will be found to divide into a 

 lateral and a medial division. 



Examine these nerves successively in the cervical, dorsal, and lumbar 

 regions. It is well, however, to defer the dissection of the sacral and 

 coccygeal nerves until the multifidus muscle has been studied. 



Cervical Region. In this region the posterior branches 

 of the spinal nerves are eight in number. The posterior 

 branch of the sub-occipital or first nerve fails to divide into a 

 medial and a lateral division. It lies deeply in the sub- 



