390 BASIS OF THE BRAIN, AND NERVES PROCEEDING FROM IT. 



and the nerves adhering to it are preserved, the olfactory or 

 first pair^**' of nerves appear on the anterior lobes, running nearly 

 parallel to each other at a small distance from the great fissure. 

 Tiiey are flat, and thin, and soft, in their texture ; their breadth 

 is rather more than one-sixth of an inch. They pass in 

 three divisions from between the anterior and middle lobes 

 of the cerebrum, which soon unite and run to the cribriform 

 plate of the ethmoid, where they expand into soft bul- 

 bous lobes, from which proceed the fibres that perforate the 

 cribriform plate, and are spread upon the Schneiderian mem- 

 brane. 



Behind the olfactory nerves are the optic. Each of which 

 comes out between the anterior and middle lobes of the cere- 

 brum ; and after blending so as to meet its fellow, turns off 

 and passes through the optic foramen in the sphenoidal bone. 

 These nerves can be traced in the brain to the thalami nerv. 

 opticorum. 



In the angle formed by the optic nerves posteriorly, is a mass 

 of softish cineritious matter (jpons Tarini) ; and also the infun- 

 dibulum which passes to the sella turcica. 



In this soft cineritious matter are two round white bodies 

 that resemble peas ; they are called the Corpora Albicantia 

 of Willis or the Eminentice Mammillares. Behind these 

 bodies are two large medullary processes, called the Crura 

 Cerebri, which are best seen if some of the cortical part of the 

 adjoining middle lobes is dissected away. They come from 

 the medulla of the opposite sides of the brain, and gradually 

 approach each other until they arrive at the tuber annulare, or 

 pons Varolii. 



The Pons Varoliif is a mass of considerable size, which has 

 a medullary appearance externally, but is striated within : it is 

 formed by the union of the two above mentioned crura cerebri, 

 and of two similar processes derived from the cerebellum, called 

 also its Crura. It lies over a part of the body of the sphenoid 

 bone, and of the cuneiform process of the occipital bone, and 



* The nerves are numbered from before. 



t Named from Varolius, physician to Gregory VIII. in 1573. 



1^^ 



