Johnston, Nen'es of Petromyzonts. 577 



then caudad and gives off branches to the ventral wall of each gill 

 sac and to the thyroid gland and blood vessels. In figs, 8 to 11 

 the IX and X nerves are seen dividing into anterior and posterior 

 branches which supply the half-gills adjacent to the arches in 

 which the nerves run. Some fibers of these nerves also reach the 

 skin of the ventral surface. 



THE CUTANEOUS COMPONENTS. 



The general cutaneous components have been traced to the skin 

 in the Golgi preparations and the results confirm the findings in P. 

 dorsatus. These components are found in the V, VII, IX and X 

 nerves. Those in the facial nerve are shown in figs. 8a and 9, 

 passing to the skin of the ventro- lateral surface below and behind 

 the orbit. Dorsal to this area the trigeminus sends fibers much 

 farther caudad, so that the trigeminus seems to encroach upon 

 the innervation territory of the facialis at first dorsally, and in 

 higher vertebrates has completely taken over the cutaneous inner- 

 vation of the facial or hyoid segment. Doubtless the appearance 

 of an operculum covering in the hyoid segment has led to the dis- 

 appearance of the cutaneous component in the facial nerve. 



The velar nerve should be specially described. As already 

 indicated, its ganglion forms the antero-mesal portion of the 

 gasserian ganglion. The ganglion cells are much smaller than 

 those of the maxillary nerve and the fibers are uniformly medium 

 fine. Beyond the ganglion the nerve bundle is compact and dis- 

 tinct from other portions of the maxillo-mandibular ganglion and 

 roots. It turns ventro-caudad on the mesal surface of the gas- 

 serian ganglion. It runs down to the velum, remaining independent 

 of the motor nerve of the "tongue" on the one hand and of motor 

 and sensory branches of the maxillaris for the roof of the mouth 

 on the other. The distribution of the nerve to the roof of the 

 velar orifice and to the tentacles is shown in fig. 12 and the endings 

 of its fibers in the border of the velum are drawn in fig, 13, I 

 have looked carefully for fibers from the VII nerve to supply at least 

 the caudal surface of the velum, but if such fibers exist they are 

 not impregnated. Along this surface of the velum lies the m, 

 velo-hyomandibularis externus w^hich is inserted in the border of 

 the velum. It is supplied by a small branch from the motor 



