338 NERVOUS SYSTEM. 



These anastomoses communicate with the intercostal veins, 

 avd, indeed, with all such as are on the outside of the spinal 

 column, by means of small branches that get out by the inter- 

 vertebral foramina. They receive the veins from the bodies 

 of the vertebrae, and from the dura and pia mater of the spinal 

 marrow. 



The two sinuses may be*traced as low down as the inferior 

 end of the sacrum, where they arise by small trunks from the 

 fatty matter which surrounds the lower end of the cauda 

 equina. When their size is somewhat augmented by their as- 

 cent, they communicate by a large transverse branch. The 

 superior end of each sinus terminates by several anastomoses 

 with the vertebral vein, and with the anterior occipital sinus; 

 through the latter of which its blood is, finally, carried into 

 the lateral sinus. For a farther account, see Sinus Verte- 

 brales. 



CHAPTER II. 



OF THE ENCEPHALON, OR BRAIN. 



BY this term is designated that section of the central portion 

 of the nervous system, which is contained within the bones of 

 the cranium. In its general configuration it differs materially 

 from the medulla spinalis, in being spheroidal or oval. It is 

 surrounded by the same membranes; to wit, the Dura Mater, 

 externally, the Tunica Arachnoidea next, and the Pia Mater, 

 internally. 



The Encephalon is formed by cineritious and medullary 

 matter, and, as a mass, consists of four distinct portions. The 

 Medulla Oblongata, which is a continuation of the spinal mar- 

 row, or its superior part; the Protuberantia Annularis, orPons 

 Varolii, which is placed at the upper extremity of the Medulla 

 Oblongata; the Cerebrum, which occupies six or seven-eighths 

 of the cavity of the cranium; and the Cerebellum, which lies 



