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bral hemisphere, deep in the median fissure (in Eugaleus on the 

 ventral surface) . Trace it forward over the dorsal surface of the 

 olfactory lobe to where it enters the nasal sac. The terminal nerve 

 is a true cranial nerve which has escaped notice until recent years. 

 It is associated with the olfactory nerve in vertebrates generally from 

 fishes to men. The fibres of the terminal nerve remain distinct from 

 those of the olfactory nerve, both in the olfactory organ and in the 

 brain. Its function is unknown. There is still a division of opinion 

 among authorities as to whether the terminal nerve should be con- 

 sidered to be a distinct cranial nerve, or a portion of the olfactory 

 nerve. 



The optic nerve can be seen at the bottom of the orbit between 

 the eye and the skull, nearly under the superior oblique muscle. It 

 arises from the ventral side of the diencephalon, passes outward, 

 penetrates the orbit at its infero-medial angle, and continues directly 

 outward to the eyeball. 



The trochlear nerve, or patheticus, penetrates the wall of the 

 orbit opposite the optic lobe. Follow it back to its origin from the 

 dorsal surface of the brain in the depression between the optic 

 lobes and the cerebellum. Then follow it from the skull to the 

 superior oblique muscle, which it innervates. 



The oculo-motor nerve arises from the ventral surface of the 

 midbrain, passes outward, and penetrates the orbit on a level with 

 and just anterior to the origins of the recti muscles. It divides im- 

 mediately into three parts; two pass to the anterior and superior 

 recti respectively, while the third passes downward along the pos- 

 terior surface of the eyeball to the inferior rectus and inferior 

 oblique muscles. In tracing this nerve the palatine process of the 

 upper jaw will be seen projecting from below into the orbit. 



The trigeminal, facial, and auditory nerves spring from the side 

 of the medulla below the corpus restiformis. The roots, and some 

 of the branches, of the trigeminal and facial nerves are so mingled 

 as to be indistinguishable except by special neurological technique. 

 The common root of the trigeminal and facial nerves shows a par- 

 tial division into a dorsal and a ventral portion; the dorsal portion 

 belongs to the facial nerve, while the ventral root is mixed. The 

 root of the auditory nerve lies close behind the trigeminal-facial 

 root, but can be distinguished fairly well. Both the trigeminal and 

 facial nerves divide into several trunks, namely: 



Trigeminal Facial 



superficial ophthalmic superficial ophthalmic 



deep ophthalmic buccal 



maxillary otic 



mandibular hyomandibular 



The superficial ophthalmic trunks of the two unite in a single 

 nerve which passes along the inner wall of the orbit above the 

 muscles of the eye to a foramen in the antero-medial angle of the 

 orbit, through which it passes to the dorsal surface of the snout. 

 The superficial ophthalmic nerve of Squalus is composed almost 

 entirely of fibres of the facial nerve. The superficial ophthalmic 

 trunk of the trigeminal gives rise to several small nerves leaving 

 the common trunk near its origin and passing to the skin above the 

 eye. The superficial ophthalmic trunk of the facial, nearly the 

 whole of the common nerve, branches profusely to supply the 

 sensory organs of the dorsal and lateral surfaces of the snout. 



The superficial ophthalmic of. Eugaleus rises from the dorsal part of the 

 trigemino-facial root and leaves the cranium by a separate foramen above and 

 anterior to the roots of the recti muscles. 



