OF THE DIPLOE. 655 



The middle thyroid vein collects the blood from the lower part of the lateral 

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

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



The facial and occipital veins have been described above. 



Surgical Anatomy. The internal jugular vein occasionally requires ligature in cases of 

 septic thrombosis of the lateral sinus from suppuration in the middle ear, in order to prevent 

 embolism of the thoracic viscera. This operation has been performed recently in several cases 

 with the most satisfactory results. The cases are generally those of chronic disease of the middle 

 ear. with discharge of pus which perhaps has existed for many years. The patient is seized with 

 acute septic inflammation, spreading to the mastoid cells, and consequent on this septic throm- 

 bosis of the lateral sinus extending to the internal jugular vein. Such cases are always extremely 

 grave, for there is a danger of a portion of the septic clot being detached and causing septic 

 embolism in the thoracic viscera. This may be mechanically prevented by ligature of the inter- 

 nal jugular vein in the middle of the neck. The operation is a comparatively simple one, and 

 may be performed by an incision similar to that employed in ligature of the common carotid 

 artery. 



The Vertebral Vein commences in the occipital region by numerous small 

 tributaries from the deep muscles at the upper and back part of the neck ; these 

 pass outward and enter the foramen in the transverse process of the atlas, and 

 descend, forming a dense plexus around the vertebral artery in the canal formed 

 by the transverse processes of the cervical vertebrae. This plexus unites at the 

 lower part of the neck into two main trunks, one of which emerges from the 

 foramen in the transverse process of the sixth cervical vertebra, and the other 

 through that of the seventh, and, uniting, form a single vessel, which 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 subclavian arterv. 



Tributaries. The vertebral vein receives in its course a vein from the inside 

 of the skull through the posterior condvloid foramen ; muscular veins 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 : the anterior and posterior vertebral veins ; and close to its termina- 

 tion it is joined by a small vein from the first intercostal space which accompanies 

 the superior intercostal artery. (See page 666.) 



The anterior vertebral vein commences in a plexus around the transverse pro- 

 cesses of the upper cervical vertebrae, descends in company with the ascending 

 cervical artery between the Scalenus anticus and Rectus capitis anticus major 

 muscles, and opens into the vertebral vein just before its termination. 



The posterior vertebral vein (the deep cervical) accompanies the profunda cer- 

 vicis artery, lying between the Complexus and Semispinalis colli. It commences 

 in the suboccipital region bv communicating branches from the occipital vein and 

 tributaries from the deep muscles at the back of the neck. It receives tribu- 

 taries from the plexuses around the spinous processes of the cervical vertebrae, and 

 terminates in the lower end of the vertebral vein. 



The 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 

 tissue. 



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

 formed only of endothelium resting upon a layer of elastic tissue, and they pre- 

 sent 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 



