490 



NETJEOLOGT. 



branch of the occipital vein, and furnishes branches leading to the 

 pterygoid veins. 



The Spinal veins are simple in their arrangement, being satel- 

 lites of the several arteries. 



The Alveolar vein has already been described as a branch of 

 the glosso-facial (see p. 447). 



CRAJSTAL KERVES. 



The nerves which are transmitted through the foramina at the 

 base of the cranium are denominated cranial nerves. They leave 

 in pairs, regularly -disposed, one on the right side and the other 

 on the left, and are named numerically, according to the order 

 in which they leave the cavity, and by names derived from the 

 parts to which they are distributed, or the functions they perform. 



The cranial nerves are differently enumerated by different 

 authorities, some dividing them into nine, and others into 

 twelve pairs. The first classification is that of Willis, who 

 makes the number correspond with the number of foramina 

 through which they find their exit ; and the last that of Soem- 

 merring, who counts the number of the apparent roots of the 

 nerves. They are also aiTanged in three divisions, according to 

 their functions, as Nerves of special sensation ; Nerves of motion ; 

 and Mixed or compound nerves — that is, nerves which contain 

 both motor and sensory fibres. Soemmerring's classification is 

 the one adopted in this work. 



DESIGNATION OF THE CRANIAL NERVES. 



