342 NERVOUS SYSTEM. 



portion of the temporal. Each of these branches is subdivided 

 into a considerable number of smaller ones, which for the most 

 part incline backwards. Their capillary terminations are sup- 

 posed by Bichat to be in small number comparatively, and to 

 be limited principally to those of nutrition. 



Some of the veins accompany the arteries, as in other parts 

 of the body, and empty into the sinuses about the base of the 

 cranium. In the case of both arteries and veins, there is, how- 

 ever, a very considerable anastomosis with the blood vessels of 

 the diploic structure of the cranium, and with those of the in- 



teguments. 



Of the Sinuses of the Dura Mater. The sinuses are large 

 cavities placed between the two larninas of the dura mater, and 

 receive the blood from the veins of the pia mater. They are 

 formed by the separation of these laminae, and are lined by a 

 membrane corresponding with the internal coat of the veins. 



1. The Sinus Longitudinalis Superior extends along the whole 

 base of the falx cerebri, from the ethmoid bone to the tento- 

 Tium, where it terminates in the lateral sinuses. It begins at 

 the foramen ccecum in a small pointed manner, and, according 

 to some anatomists, by a small vein, which passes from the nose 

 through this foramen; it is successively increased in size from 

 before backwards, and is of a prismatic shape. One side of the 

 prism is upwards, and, of course, is formed by the external la- 

 mina of the dura mater; while the other two parietes are late- 

 ral, and are formed by the duplicature of the internal lamina. 

 Its cavity presents a number of small cords, round or flattened, 

 passing from one side to the other; they are called Chords Wil- 

 lisii or Trabeculse, and prevail principally at its back part. 



The longitudinal sinus receives on each side from ten to twelve 

 large veins, which bring the blood from the pia mater. Those 

 from the convex surface of'the brain are joined just before enter- 

 ing the sinus by such as belong to the flat side of the hemispheres. 

 These veins enter the sinus, for the most part, obliquely forwards, 

 or in a manner opposed to its circulation. They are also fur- 

 nished with valves, which circumstance, besides their oblique 

 entrance into the sinus, is a provision against their being filled 

 by the regurgitating blood. The most posterior ones previous- 



