460 VEIXS OF THE HEAD AXD NECK. 



(i) The pharyngeal vein commences at the back and sides of the pharynx, and 

 sometimes ends in the superior thyroid vein, and at other times in the lingual, or 

 separately in the internal jugular vein. 



(c) The occipital vein, corresponding in course and distribution with the occipital 

 artery, communicates with a plexus of veins upon the occiput, and terminates occa- 

 sionally in the external jugular A^ein, but more frequently in the internal. 



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



(?) The laryngeal vein receives branches from the larynx through the thyro-h} r oid 

 membrane, and opens into the internal jugular, the common facial, or sometimes into 

 the superior thyroid vein. 



(/) The superior thyroid vein commences by branches in the thyroid body, 

 in company with those of the superior thyroid artery, and runs transversely 

 outwards. 



(g) The middle thyroid vein, likewise derived from the thyroid body, is placed 

 lower than the superior thyroid. 



VENOUS CIRCULATION WITHIN THE CRANIUM. 



The part of the venous system contained within the skull consists of 

 veins properly so called, and of certain channels called 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. 



CEREBRAL VEINS. 



The veins of the brain are divisible into those which ramify upon its sur- 

 face, and those which are placed within its ventricles. 



The superficial veins upon the upper surface of the hemispheres are for 

 the most part lodged in the tortuous sulci between the convolutions ; but 

 some run over the convexity of the convolutions. Their general direction is 

 towards the middle line ; and, on reaching the margin of the longitudinal 

 fissure between the hemispheres, they receive branches from the flat mesial 

 surface of the hemispheres, and, becoming invested by tubular sheaths of 

 the arachnoid membrane, incline obliquely forwards and open in that 

 direction into the superior longitudinal sinus. 



The veins upon the sides and under surface of the brain are directed 

 outwards, to open into the lateral and other sinuses at each side. 



The deep veins of the brain commence by branches within the ventricles 

 of that organ. Upon the surface of the corpus striatum, for example, 

 several small venous branches are seen, which for the most part converge 

 to form a slender vein which runs along the groove between the corpus 

 striatum and optic thalamus, and opens into one of the veins of the choroid 

 plexus. The minute veins of the choroid plexus pass backwards, and incline 

 towards the middle line from each side, so as to form, by their union, two 

 veins vence Galeni. These, lying parallel, run directly backwards, enclosed 

 within the velum interpositum, and escape from the interior by passing 

 through the great transverse fissure of the brain between the under surface 

 of the corpus callosum and the tubercula quadrigemina. In this way they 

 reach the anterior margin of the tentorium cerebelli, at its place of union 

 with the falx cerebri, where they terminate by opening into the straight 

 sinus. 



The veins of the cerebellum are disposed in two sets. Those of the 

 upper surface incline inwards and forwards for the most part, and run 

 upon the upper vermiform process, over which they ascend a little to reach 

 the straight sinus, in which they terminate ; some, farther forward, open 



