386 Journal of Comparative Neurology. 



short distance a portion of the first root of the r. lateralis 

 accessorius, as already described. After the separation 

 of those communis fibres, it still contains about as many 

 fine as coarse fibres (about 30 of each). The meningeal 

 .branches described by several authors as arising from the 

 IV nerve in several types of animals probably are ulti- 

 mately derived from similar anastomoses v^ith communis 

 roots. After the emergence from the cranium of the 

 V+VII complex the trochlearis continues intra-cranially 

 in the same relation to the brain as before. 



At the level of the optic chiasm it pierces the cranial 

 wall, which is here membranous, then, turning dorsad, it 

 follows the outer wall of the cranium under the supra- 

 orbital trunk, the finer fibres gathering on the dorsal side 

 of the nerve. These relations maintain along the outer 

 side of the intemasal cartilage until the m. obliquus supe- 

 rior is reached, to the dorsal surface of which the nerve 

 passes and into which it begins to send nerve fibres. The 

 finer fibres, however, separate and run along the dorsal 

 surface of the muscle to supply the smaller muscle fibres 

 which occupy the dorsal edge of the muscle. 



IV. — The N. Oculomotorius. 



In conformity with the enormous size of the eye, the 

 third nerve is also large. Its nucleus lies far dorsad near 

 the median line, in part mesially of the large fasciculus 

 longitudinalis dorsalis, but also, as it were, squeezed out 

 so that a large part of it lies under the endyma of the floor 

 of the mesocoele dorsally of the fasciculus and some also 

 ventrally of it. Some fibres also plainly come from the 

 fasciculus itself. Its origin being concealed in projection 

 by the V + VII ganglionic complex, is not shown upon 

 the plots. 



