394 NERVOUS SYSTEM. 



ter, when examined from the upper surface, has its foramina 

 arranged into two rows, one next to the crista galli, and the 

 other next to the cellular portion of the ethmoid. Each row 

 consists of about six or eight foramina, and between these rows 

 there are other foramina, smaller, and not so much in a line 

 with each other. The same cribriform foramina, when exa- 

 mined from the cavity of the nose, are more numerous, espe- 

 cially those belonging to the first two rows, in consequence of 

 the latter branching out below into several canals, which may 

 be seen very distinctly on the side of the base of the nasal la- 

 mella, and on that of the cellular portion of the ethmoid. 



The distribution of the olfactory nerve corresponds with this 

 arrangement of the cribriform plate, for it has three rows of 

 branches proceeding from the under surface of its bulb, each 

 branch going through its appropriate foramen, and subdividing 

 in it, but sometimes two filaments pass through the same fora- 

 men. In a short space after their origin, they become invested 

 by sheaths of the dura mater, which are extended a considera- 

 ble distance, and which, by a close adhesion to the nerves, 

 make them appear much larger below than they are at the 

 roots. When the nerves reach the cavity of the nose they 

 anastomose together, and descending between the bone and 

 the pituitary membrane, they ramify into an infinitude of small 

 branches, the terminating filaments of which reach the nasal 

 surface of the membrane. 



The Internal Branches, or those next to the crista galli, di- 

 verge from the cribriform plate, and pass downward between 

 the septum and the pituitary membrane: where they first appear 

 in the nose, there are some few adhesions or anastomoses be- 

 tween them; but their filaments afterwards keep perfectly dis- 

 tinct, and, spreading themselves out on the pituitary membrane 

 of the septum, make an appearance resembling a flat camelV 

 hair pencil. The middle ones are the longest, and may be 

 traced almost to the floor of the nose; the anterior are shorter 

 somewhat; the posterior do not reach obviously below the mid- 

 dle of the septum. 



The External Branches have a very different mode of distri- 

 bution. While still in their canals they divide into many fila- 

 ments, which anastomose frequently with each other, and when 

 they have fairly got into the cavity of the nose, the same fre- 



