superficiol ophthalmic VII 

 ophthalmic profundus (Vi) 



pineal stalk 



cerebellum 



dorsal sensory line nerve 



spinoccipital nerves 



1st spinal nerve 



lateral line X 



alX 



olfactory tract from bulb 



maxillary branch, V2 



buccal branch VII 

 palatine branch VII 

 mandibular branch, V3 



hyomandibular branch VII 



hypoglossal nerve (XII) 



Figure 13-14. Cranial nerve distribution in Squa/us aconfhios. (After Norris and Hughes, 1920} 



there is a small infundibulum ending in an undifferentiated 

 saccus vasculosus. There are small bilateral lobi inferiores. 

 The anterior lobe of the pituitary is small and inconspicu- 

 ous. The pars nervosa of the infundibulum is undifferen- 

 tiated. 



The cranial nerves are like those of other groups with the 

 exception that the three eye-muscle nerves are lacking (the 

 oculomotor, the trochlear, and the abducens) along with the 

 muscles of the vestigial eye (Figure 13-18). The olfactory 

 nerve is represented by a large number of bundles passing 

 directly from the wall of the nasal capsule into the olfactory 



bulb. The olfactory bulbs and cerebral lobes have narrow 

 ventricles connected by equally narrow passages (foramina 

 of Monroe) with the restricted third ventricle. The optic 

 nerves are very small and cross within the substance of the 

 diencephalon, which appears to extend forward beneath the 

 telencephalic lobes to touch the olfactory bulbs. 



The fifth nerve has a number of branches which corre- 

 spond only partly to the branches observed in the gnatho- 

 stomes. The seventh nerve is small and quite separate from 

 the fifth; it can be presumed that fibers from the seventh 

 pass out through the divisions of the fifth nerve. The eighth 



pineal 



telencephalon 



right hobenula 

 (saccus dorsolis 

 removed) 



optic lobe 

 V 



optic lobe 

 posterior commissure 

 saccus dorsolis 

 pineal 



chorioid roof of third 

 and fourth ventricle 



fourth ventricle 



parietal 

 organ 



I cord 



olfoctory bulb' 



anterior commissure 

 foramen of Monroe 



optic nerve 



cerebellum 



pttuitory 



saccus voscul 



losus 



A^ c 



-2nd spinal 



B 



Figure 13-15. Brain and cranial nerve roats af the lamprey. A, dorsal view including, on the right, 

 the eye ond its musculoture and the ear capsule; B, medial view of right half of the brain. 



398 • THE NERVOUS SYSTEM 



