THE VEINS OF THE CEKEBRUM. 519 



the tongue, the surrounding muscles, the sublingual gland, and the mucous mem- 

 brane of the floor of the mouth ; 2, two vena comites of small size which accompany 

 the lingual artery ; and 3, the dorsal veins of the tongue, which proceed from a plexus 

 beneath the mucous membrane on the posterior third of that organ. These vessels 

 are sometimes united in a short common trunk, but more frequently they open sepa- 

 rately into the internal jugular or common facial vein. 



(d) The common facial vein has already been described. 



(e) The superior thyroid vein leaves the upper part of the thyroid body, after 

 communicating freely with -the other thyroid veins, and ascends to join the internal 

 jugular or frequently the common facial vein. It receives branches from the sur- 

 rounding muscles, and the superior laryngeal and crico-thyroid veins. 



(/) The middle thyroid vein issues from the lateral lobe of the thyroid body, and 

 crosses the common carotid artery to join the internal jugular vein on a level with, 

 or a little below, the cricoid cartilage. 



VENOUS CIRCULATION WITHIN THE CRANIUM. 



The part of the venous system contained within the skull consists of veins pro- 

 perly so called, and of certain channels named sinuses, which receive the blood from 

 those veins, and conduct it to the internal jugular veins. The sinuses alluded to 

 are spaces left between the layers of the dura mater, the fibrous covering of the 

 brain. 



VEINS OF THE BRAIN. 



The veins of the cerebrum are more numerous than, and for the most part 

 run independently of, the arteries. They have very thin walls, and communicate 

 freely together. They are divided into superficial, which ramify upon the surface of 

 the hemispheres, and deep, which are placed within its ventricles and emerge by the 

 transverse fissure. The former are again subdivided into superior and inferior. 



The superior cerebral veins, ten to twelve on each side, run inwards over the 

 upper surface of the large brain to the margin of the longitudinal fissure, where they 

 are joined by branches which ascend on the mesial surface of the hemisphere, and 

 then open into the superior longitudinal sinus. The anterior veins are small, and 

 are directed transversely inwards ; the middle and posterior are larger, pass obliquely 

 forwards, and finally are embedded for a short distance in the wall of the sinus before 

 opening into its cavity. 



The inferior cerebral veins pass from the outer and lower surfaces of the hemi- 

 sphere to the cavernous, superior petrosal and lateral sinuses. One of these vessels, 

 known as the middle cerebral or superficial Sylvian vein, is of large size, and courses 

 superficially along the fissure of Sylvius to end in the cavernous sinus : it collects 

 branches from the frontal, parietal and temporal lobes. The great anastomotic vein 

 of Trolard is formed by one of its tributaries on the surface of the parietal lobe, becom- 

 ing continuous with a superior cerebral vein ascending to the superior longitudinal 

 sinus. A similar posterior anastomotic vein extends from the middle cerebral down- 

 wards and backwards across the temporal lobe to the lateral sinus (Labbe). 



The deep cerebral veins are collected into two trunks, which are known as the 

 veins of Galen. These vessels begin close to the foramen of Monro, being formed on 

 each side by the union of the choroid vein, which ascends tortuously along the margin 

 of the velum interpositum from the inferior cornu of the lateral ventricle, returning 

 the blood from the choroid plexus of that cavity, and the vein of the corpus strialum^ 

 which passes forwards in the groove between the corpus striatum and optic thalarnus, 

 being joined in its course by branches from both these bodies, and near its termina- 

 tion by veins from the septum lucidum and the anterior cornu of the ventricle. The 



