356 HEAD AND NECK 



the posterior branch enters the triangle from beneath its 

 lower border. For the relations of the fourth part see above 

 and p. 443. 



Branches. No branch of importance is given off from 

 the first part. The second part gives off lateral spinal 

 (p. 193) and muscular branches. The branches from the 

 third part are muscular twigs, and branches to anastomose 

 with twigs from the occipital and the deep cervical arteries. 

 The fourth part gives off a meningeal branch before it 

 perforates the dura mater and, afterwards, a series of branches 

 to the central nervous system (see pp. 443, 444). 



Vena Vertebralis. Only the first part of the vertebral 

 artery is accompanied by a definite vertebral vein. There 

 are no accompanying veins with the fourth part of the artery, 

 but a plexus is formed round the commencement of the 

 third part, by the union of tributaries from the venous plexus 

 in the vertebral canal and from the plexus of veins in the 

 sub-occipital triangle. This plexus accompanies the second 

 part of the artery through the transverse processes of the 

 cervical vertebrae ; it anastomoses with the venous plexuses in 

 the vertebral canal ; and it terminates below in one or two 

 vertebral veins ; these accompany the first part of the artery 

 and end in the posterior aspect of the commencement of the 

 innominate vein. 



Dissection. The muscles must now be completely removed, in order 

 that the vertebral and cranio-vertebral joints, and the ligaments in con- 

 nection with the cervical portion of the vertebral column may be examined. 



THE JOINTS OF THE NECK. 



The epistropheus, atlas, and occipital bone present a series 

 of articulations in which the uniting apparatus is very different 

 from that of the vertebrae below. 



Articulations of the Lower Five Cervical Vertebrae. The 

 lower five cervical vertebrae are united together very much 

 upon the same plan as the vertebrae in other regions of the 

 vertebral column. Both the bodies and the vertebral arches 

 are connected by distinct articulations and special ligaments. 



Three separate joints may be said to exist between the 

 opposed surfaces of the bodies of two adjacent cervical 

 vertebrae viz., a central synchondrosis and two small lateral 

 diarthrodial joints. 



