THE SEGMENTAL VALUE OP THE CRANIAL NERVES. 145 



portio minor of the ramus ophthalmicus superficialis 1 is rather more ex- 

 tensively connected with this nerve than is usually the case. The 

 nerve which Midler marks y, and calls the " ophthalmic branch of the 

 fifth," but which he does not seem to have followed to the brain, I 

 see no reason for considering as other than what one would naturally 

 suppose it to be from its distribution to all the eye-muscles except the 

 rectus externus, i.e. the combined third and fourth nerves. In Midler's 

 figure 2 there is a remarkable point of difference, inasmuch as the 

 nerve which I have considered in the former figure to be the proximal 

 part of the portio minor, or trigeminal portion of the ramus ophthal- 

 micus superficialis, is entirely omitted. No mention is made either in 

 the text or in the description of the figures of this very important 

 difference. I would further notice that, although the two figures in 

 question are drawn of the same size and to the same scale, yet that 

 the relative proportions of the several nerves, and more especially the 

 extent to which they are fused with one another, are so very different 

 in the two cases that one is driven to suppose either that the figures 

 are taken from different specimens, in which case there must be con- 

 siderable individual variability in the very points alleged to be excep- 

 tional, or else that one or others of the figures is taken from an 

 incomplete dissection. 



The above considerations lead to the conclusion that, in the absence 

 of direct confirmation, Midler's account of the eye-muscle nerves in 

 Lepidosteus does not prove that they are in any way exceptional, 

 except in the fact of the third and fourth nerves entering the orbit as 

 one trunk. 



Very important information concerning these nerves in Lepidosteus 

 has recently been afforded by Schwalbe, who finds, from a careful 

 examination of the nerves and brain, that both the third and fourth 

 nerves have independent origins from the brain;' 1 a fact which, as in 

 the case of Petromyzon, must be held to conclusively prove that such 

 connection as may actually occur between the fifth nerve on the one 

 hand, and the third and fourth on the other, beyond their roots of 

 origin, is of a purely secondary character, and that it does not in the 

 very slightest degree militate against the claims of the third and 

 fourth to rank as independent cranial nerves. 



1 For the nomenclature of these ophthalmic nerves, vide Marshall and Spencer, " Obser- 

 vations on the Cranial Nerves of Scyllium," part i., Quart. Joum. of Micros. Science, 

 July 1881. 



a Schwalbe, Das Ganglion Qculomotorii, pp. 23, 72, and 73. 

 L 



