THE NERVOUS SYSTEM 137 



sphenoid (cf. Gaupp, 1 9 1 1), at about the level, or just in front of, the 

 optic nerve and dorsal to it. The nerve may divide within the skull 

 and pass through its wall as a double nerve, otherwise it divides 

 immediately on emerging from its foramen, and before penetrating 

 the origin of the M. levator bulbi. The division is unequal, one 

 branch being very much finer than the other. The finer branch (IVb, 

 Hoffmann) passes at once through the origin of the M. levator 

 bulbi, and goes to the M. obliquus superior without anastomosing 

 with any branch of the trigeminal nerve. It may come into contact 

 with such a branch but it is comparatively easily separable from it, 

 and no exchange of fibres appears to take place. The larger branch 

 usually turns a little anteriorly before penetrating the origin of the 

 M. lev. bulbi, and after it has emerged from this muscle it always 

 comes into contact, and apparently anastomoses with, one or more 

 cutaneous twigs of the R. ophthalmicus profundus V. It may divide 

 into several twigs, some of which anastomose with branches of the 

 Vth nerve while others pass to the M. obi. sup., or it may anastomose 

 as a whole with a branch from the trigeminus, in which case fibres 

 arise from the combined nerve and enter the superior oblique muscle. 



The above description agrees fairly well with that given by Hoff- 

 mann, except that no anastomosis between the trochlearis and the 

 trigeminus ?7iesial to the M. lev. bulbi such as he describes has been 

 found, neither in fact has any branch of the Vth nerve been found 

 which could fuse with it in this position. It should be noted here that 

 Coghill (1902) describes the trochlearis of Amblystoma meeting a 

 trigeminal branch mesial to the M. lev. bulbi. He says, 'I find no 

 positive evidence of an anastomosis in this case although the nerves 

 are in very intimate relation with each other. The fourth nerve is 

 penetrated by the trigeminal twig and then passes through the M. 

 lev. bulbi and innervates the M. obliquus superior.' This author, 

 however, does not describe any fusion of the two nerves lateral to the 

 M. lev. bulbi, nor any division of the trochlearis into two distinct 

 rami such as occurs in Salamandra. 



From the above details the following facts emerge: 



(i) A N. trochlearis does occur in Salamandra and the M. obliquus 

 superior is innervated by it. 



(ii) The whole of the fourth cranial nerve is not distributed to the 

 eye muscle, but some part of it goes to the skin or underlying tissues 

 via the track of a trigeminal twig.^ 



' If Hoffmann's account is correct these apparently cutaneous branches of the troch- 

 learis may actually come from the fifth twig, which, according to him, joins the troch- 

 learis mesial to the M. levator bulbi. 



