THE SUPERIOR CAVAL SYSTEM. 867 



3. The Lingual Vein. — The lingual vein (v. lingualisj is a short trunk which 

 either opens directly into the internal jugular or unites with the facial vein to form a 

 linguo facial trunk. It is formed by the union of two vessels, the deep lingual veins, 

 which are the ven^e comites of the lingual artery, and the sublingual. 



The deep lingual veins are of small calibre and accompany the lingual artery 

 throughout its entire course, numerous cross-connections between them involving the 

 artery as in a plexus. Shortly before opening into the lingual stem the two veins unite, 

 and into the vessel so formed the companion veins of the dorsal artery of the tongue 

 (vv. dorsales linguae) open, these vessels communicating with the tonsillar plexus and 

 the superior laryngeal vein. 



The sublingual vein, also termed the ranine, has its origin on the under sur- 

 face of the tip of the tongue, beneath the mucous membrane. It passes backward, 

 at first in company with the submaxillary, duct, and, after receiving communicating 

 branches from the deep lingual and the submental veins, it passes to the outer side 

 of the hyoglossus muscle and continues backward in company with the hypoglossal 

 nerve, whence it has been termed the v. comitans n. hypoglossi. 



All the branches of the lingual vein are provided with valves. 



Variations. — Considerable variation exists in the extent to which the lingual vein is de- 

 veloped, both its constituent tributaries as well as the dorsales linguae sometimes opening inde- 

 pendently into the internal jugular. It may open into either the external or anterior jugular 

 instead of the internal, and the deep linguals may open into the pharyngeal vein. Occasionally, 

 by the enlargement of the connection normally occurring, the submental vein becomes a tribu- 

 tary of the sublingual. 



4. The Superior Thyroid Vein. — The superior thyroid vein (v. thyreoidea 

 superior) accompanies the artery of the same name. It arises in the upper portion 

 of the plexus which encloses the thyroid gland, communicating through it with its fellow 

 of the opposite side and with the middle and inferior thyroid veins. It is directed up- 

 ward and backward, and opens either directly into the internal jugular or more usually 

 into the lingual or the linguo-facial trunk. 



Tributaries. — The following are received by the superior thyroid vein, [a) The superior 

 laryngeal vein (v. laryngea superior), which arises in the pharyngo-laryngeal recess from a plexus 

 which receives the blood from the aryepiglottidean fold and the laryngeal musculature and com- 

 municates with the vv. dorsales linguae above and also with the lower portion of the pharyngeal 

 plexus. It passes upward and backward in company with the corresponding nerve and artery 

 and opens into the superior thyroid vein or occasionally into the linguo-facial trunk or the 

 anterior jugular, {b) The crico-thyroid vein is a slender vessel which accompanies the artery 

 of the same name, (r) The sterno-mastoid vein (v. sternocleidomastoidea) receives blood from 

 the sterno-cleido-mastoid muscle and is associated with the artery of the same name. 



5. The Middle Thyroid Vein. — The middle thyroid vein is not always 

 present and may be regarded as accessory to the superior thyroid. It issues from 

 the thyroid plexus, opposite the lower part of the lateral lobe of the gland, and passes 

 downward and outward, independently of any artery, to open into the internal jugular 

 at the junction of its middle and lower thirds. 



The Sinuses of the Dura Mater. 



« 



The sinuses of the dura mater (sinus durae matris) form a series of channels, 

 frequently of considerable size, occupying clefts in the substance of the dura mater. 

 They receive the cerebral, meningeal, and diploic veins and, in addition, communicate 

 with the extracranial veins by numerous connecting veins known as emissary veins, the 

 largest and most important of which are the ophthalmic veins. They are drained 

 mainly by the internal jugular. A statement of their general structure and a brief 

 description of the blood-lakes associated with them have already been given (page 851). 



I. The Lateral Sinus. — The lateral sinus (sinus transversus) (Figs. 756, 757) 

 has its origin opposite the internal occipital protuberance, at which point there is a 

 meeting of five sinuses, the two lateral, the superior longitudinal, the straight, and 



