540 



VEINS. 



lobe of the thyroid gland, and, being joined by some branches from the larynx 

 and trachea, terminates in the lower part of the internal jugular vein. 



The occipital vein has been described above. 



The Vertebral Vein commences in the occipital region, by numerous small 

 branches, from the deep muscles at the upper and back part of the neck, passes 

 outwards, and enters the foramen in the transverse process of the atlas, and 

 descends by the side of the vertebral artery, in the canal formed by the trans- 

 verse processes of the cervical vertebrae. Emerging from the foramen in the 

 transverse process of the sixth cervical, it terminates at the root of the neck in 

 the back part of the innominate vein near its origin, its mouth being guarded 

 by a pair of valves. On the right side, it crosses the first part of the subcla- 

 vian artery. This vein, in the lower part of its course, occasionally divides 

 into two branches, one of which emerges with the artery at the sixth cervical 

 vertebra ; the other escapes through the foramen in the seventh cervical. 



Branches. The vertebral vein receives in its course the posterior condyloid 

 vein, muscular branches from the muscles in the prevertebral region ; dorsi- 

 spinal veins, from the back part of the cervical portion of the spine ; meningo- 

 rachidian veins, from the interior of the spinal canal; and lastly, the ascending 

 and deep cervical veins. 



VEINS OF THE DIPLOE. 



The diploe of the cranial bones is channelled, in the adult, by a number of 

 tortuous canals, which are lined by a more or less complete layer of compact 



Fig. 304. Veins of the Diploe, as displayed by the Removal of the Outer Table of the Skull. 



tissue. The veins they contain are large and capacious, their walls being thin, 

 and formed only of epithelium, resting upon a layer of elastic tissue, and they 

 present, at irregular intervals, pouch-like dilatations, or culs-de-sac, which serve 

 as reservoirs for the blood. These are the veins of the diploe : they can only 

 be displayed by removing the outer table of the skull. 



In adult life, as long as the cranial bones are distinct and separable, these 

 veins are confined to the particular bones; but in old age, when the sutures are 

 united, they communicate with each other, and increase in size. These vessels 

 communicate, in the interior of the cranium, with the meningeal veins, and 

 with the sinuses of the dura mater ; and on the exterior of the skull, with the 



