ON EMBRYOLOGY AS AN AID TO ANATOMY 43 



who has dissected a head and neck. The problem 

 to which I refer is that of the nerve supply of the 

 muscles by which the various movements of the 

 eyeball are effected. 



Whoever has dissected the orbit cannot fail to 

 have been struck with the large number of nerves 

 which not only traverse it but supply parts con- 

 tained therein ; and also with the additional fact 

 that these are either distinct nerves or branches of 

 distinct nerves, and not merely separate branches 

 of one or two cranial nerves. Thus, of the 

 twelve cranial nerves no less than six are dis- 

 tributed wholly or in part to the contents of the 

 orbit. When we consider that of the remaining 

 six, two the olfactory and the auditory are 

 nerves of very special function and limited dis- 

 tribution, and that another one the spinal 

 accessory has but slight claim to be considered 

 a cranial nerve at all, the fact becomes still more 

 striking. A further and far more significant fact 

 than the above is that of these six nerves four 

 are exclusively distributed to the orbit, and send 

 branches nowhere else. Of these four nerves 

 one is the optic nerve, while the other three supply 

 the muscles by which the movements of the eye 

 are effected. I must ask your indulgence for a 

 moment if I refer to such an exceedingly familiar 

 fact as the arrangement and distribution of these 

 muscles and their nerves. I only do this because 

 it is absolutely necessary to the argument I wish 

 to put before you that this arrangement and 

 distribution should be fresh in your minds. 



