76 DR KNOX on the Comparative Anatomy of the Eye. 



the cornea. They found nerves going towards the ciliary muscle, 

 which were lost at the point where the muscle is inserted into 

 the sclerotic : they imagined, therefore, that these nerves must 

 be distributed to the cornea, as it was difficult to conceive how 

 any should be sent to the sclerotic. 



I am fully convinced, from numerous dissections, that the so 

 named ciliary ganglion in man, and in the mammalia, is a pure 

 fiction, and imagined with a view to support the hypothesis of 

 the iris being altogether an involuntary muscle. As it is my in- 

 tention to resume the subject shortly, I shall here merely ob- 

 serve, that nervous plexuses, as those with which the nerves of 

 the extremities are connected in the mammalia, and the iridian 

 nerves in birds, are placed there by nature, not to impede the 

 influence of the brain, exercised during volition, over the muscles 

 to which these nerves are respectively distributed, but to afford 

 a more extensive point of connection to a much greater number 

 of nervous trunks than could have been the case, had the 

 branches connecting the plexus with the brain and spinal mar- 

 row, proceeded uninterruptedly to their termination in the re- 

 spective organs. The same observation is applicable, slightly 

 modified, to the ganglia found in the course of the cerebral 

 nerves, and in those of the vertebral column ; it is to the sym- 

 pathetic system of nerves, and their ganglia only, that the disco- 

 very of our celebrated countryman JOHNSON is applicable. It 

 must be evident to the Society, that to enter further into the 

 discussion of these doctrines, would lead me quite from the sub- 

 ject of the Memoir. 



The nerve proceeding towards the choroid gland in fishes, is 

 a branch of the third, and not of the fifth ; moreover, it cannot 

 be traced to the gland. The remaining branches of the third are 

 distributed to the external muscles of the eye-ball. The sixth 

 pair of cerebral nerves in fishes join the fifth within the cranium. 



