119 



affected by the torsion of the head, since the parasphenoid 

 and its eye muscle canal are simply rotated en hloc to the 

 rig-ht along their longitudinal axes. The distribution of 

 the nerves is therefore the same, except that those of the 

 left side have been swung upwards so as to lie nearer the 

 dorsal edge of the body, and hence above those of the right 

 side. In the case of the branch to tlie inferior oblique 

 this rotation has caused the left one to be situated at first 

 much above the right. In front, however, it begins to 

 turn downwards towards the parasphenoid, and the right 

 one at the same time rising, they eventually take up cor- 

 responding positions at the sides of the parasphenoid and 

 ethmoid cartilage. Finally the left turns upwards to 

 reach its muscle in which it breaks up in much the same 

 wajr as the right. Neither of the long eye muscle nerves 

 (patheticus and the branch just described) of the left side 

 reaches, at its final distribution, a much higher transverse 

 level than that of the right. 



If a comparison be made with the eye muscle nerves 

 of Menidia, as described by Herrick, it will be seen that 

 in the two forms the relations of the nerves are essentially 

 the same. 



N e r V u s patheticus s . t r o o h 1 e a r i s — lY. 



The fourth nerve of the right side (iv. o.s.) consists of 

 many large and a few small fibres all heavily myelinated. 

 It has no connection with the communis vii. as described 

 by Herrick in Menidia. The nucleus of the pathetic is 

 situated dorsally close behind that of the oculomotor. The 

 two pathetic nerves cross over the mesocoele as in all 

 hitherto investigated vertebrates, so that, for example, the 

 rig-ht nerve arises from the left side of the brain. The two 

 nerves pass first backwards, then rise sharply over the 

 mesocoele, cross, and leave the braiu almost in the same 



