SCYLLIUM CANICULA 



259 



The foramina through which these nerves leave the 

 cranium have already been dealt with, so that the next point is to 

 consider their distribution. The first, or olfactory nerve, passes 

 through the posterior wall of the olfactory capsule as a series of fibres 

 which are distributed to the olfactory epithelium. The second, or 

 optieus, passes through the side wall of the orbit, up to the optic stalk, 

 and is distributed to the retina. The third, or oculomotor ius, also 

 perforates the orbital wall and supplies the superior, internal and 

 inferior oblique muscles of the eyeball. The fourth, or patheticus, 

 enervates the superior oblique eye muscle. The fifth, or trigeminus, 

 after leaving the ganglion, divides into two branches inside the 

 cranium, of which the anterior, a sensory branch, passes out into 

 the orbit as the ophthalmic branch of the fifth nerve. This runs 

 forward along the mesial dorsal wall of the orbit and out through 

 its roof to the skin of the dorsal side of the front end of the head and 

 snout. The posterior branch enters the orbit by a common foramen 

 with the sixth and part of the seventh nerves, and quickly divides 

 into two, the maxillary and mandibular nerves. They pass antero- 

 laterally across the floor of the orbit, and the former goes to the skin 

 and muscles of the upper jaw and lip, while the latter spreads out 

 in the skin and muscles of the lower jaw. The sixth nerve, or 

 abducens, goes to the external rectus muscle. 



So far the distribution of the cranial nerves has been typical, 

 but when we come to the seventh, or facial nerve, we find a striking 

 difference between Scy ilium and Rana. In the first place it is really 

 a mixture consisting of the branches of the facialis proper, such as 

 we find in all Craniates and another series of fibres belonging to the 



