Chap. 28,] Origin of the Nerves. 183 



perforations of that bone. Afterwards-being joined by 

 a branch- from the fifth pair, they are fpread on the 

 internal membrane of the nofe, and conftitute the organ 

 offmelling. 



The fecond pair of nerves is the optic, which are 

 continued from the thalami nervorum opticorum, and 

 are of a iarge fize ; they firft make a large curve out- 

 Wards, and then run obliquely inwards and forwards, 

 till they unite at the fore part of the fella turcica; they 

 then divide, and each runs to its proper foramen in th<* 

 fphenoid bone. They are accompanied to the eye by 

 the ocular artery, and are at length expanded into the 

 tender and pulpy fubftance of the retina, which re- 

 ceives the impreffions of light. The union of the optic 

 nerves has been thought to explain fome phenomena 

 of vifion, as our feeing objects fmgle with two eyes, 

 and their uniform motion. The union of the optic 

 nerves generally appears fo confiderable, that fome 

 anatomifts have thought that they decuffated each other, 

 and went to the eye on the oppofite fide of the head 

 from that whence they arofe. In many fifhes the 

 optic nerves evidently crofs each other, but this does not 

 feem to be the cafe in man. They are inferted into 

 the eyes, not directly at their pofterior part, but rather 

 towards that fide which is placed next the nofe. We 

 are unable to fee with that part of the retina where the 

 optic nerve enters. 



The third pair called motores oculi arifes from the 

 crura cerebri, near the pons Varolii ; they run along the 

 fide of the fella turcica, and pafs out at the foramina 

 lacera, after which each of them divides into branches ; 

 one of thefe, after forming a ganglion, is diftributed 

 to the globe of the eye ; the others are fent to the muf- 

 culus rectus of the palpebra, and to the attollens, ad- 

 ductor, 



