THE BRAIN AND ITS APPENDAGES. 127 



receiving various muscular branches in its course, also the 

 medullary vein of the tibia. 



The femoral vein results from the two last named vessels; 

 runs behind the femoral artery, and ends in the external iliac 

 vein. It receives muscular veins, as well as veins from the 

 stifle joint, and the medullary vein of the os femoris j also, 

 about two thirds of its length upwards, it is joined by the 

 saphena vein. 



The vena saphena major results from the large metatarsal 

 vein ; at the hock it anastomoses with the anterior tibial vein ; 

 it also receives cutaneous and muscular branches in its course. 



The vena saphena minor springs from the small metatar- 

 sal vein ; it runs up the back of the hock, over the root of 

 the os calcis, and ultimately reaches the femoral vein. 



The vena porta circulates the blood through the liver, and 

 is principally formed by the union of the splenic and mesen- 

 teric veins. 



THE BRAIN AND ITS APPENDAGES. 



The cerebrum, cerebellum, and medulla oblongata, and 

 medulla spinalis are invested with three membranes : the du- 

 ra mater, pia mater, and tunica arachnoides. Of these the 

 exterior is the dura mater : which, though called a membrane, 

 is of a dense, tough, and inelastic texture. It is so firmly 

 adherent, by means of numerous little prominences, to the 

 sutures of the cranium, that it is difficult to separate them ; 

 this membrane is to the internal cranium what the pericrani- 

 um is externally. The inner surface of the dura mater is 

 lubricated by a fluid furnished by its own blood-vessels. 



The pia mater is that membrane which closely envelops the 

 substance of the brain, and dips down between its convolutions, 

 and adheres to its surface by numberless minute blood-ves- 

 sels. It differs in its appearance and texture from the dura 

 mater ; presenting a smooth surface exteriorly, but a rough 

 and villous one next to the brain, and being composed of a 

 beautiful network of blood-vessels united together by a deli- 

 cate cellular tissue. 



