CRANIAL NERVES. 173 
ularis passes behind it and hence is a post-trematic ramus. In some 
cases a small twig bends down from the palatine and represents the 
pretrematic branch. 
Three of these—ophthalmicus superficialis, buccalis and mandib- 
ularis externus—belong to the lateralis system, which is unrepre- 
sented inthe spinal nerves. This has its own ganglion, which may unite 
with geniculate or semilunar, and it supplies the lateral line system of 
the head (see sense organs). The superficial ophthalmic innervates the 
supraorbital line of these organs, and in the elasmobranchs, breaks 
up distally to go to the modified organs (ampulle of Savi and Loren- 
zini) at the tip of the snout. In the same way the buccalis supplies 
the infraorbital line and the mandibularis externus those of the lower 
jaw and the hyoid and spiracular regions. 
As there are no myotomic muscles in the region supplied by the 
facial nerve, there are no somatic motor components The general 
cutaneous elements run in the hyoideus to the skin of the hyoid region, 
but in other vertebrates this territory is supplied by branches of the fifth, 
which spread to the operculum and to the dorsal surface of the head. 
The visceral motor components occur in the hyoid nerve and, in the 
aquatic forms, they supply the muscles of the hyoid region and the 
posterior belly of the depressor mandibule. In the mammals, with 
the development of the muscles of expression (p. 134), the same 
branch (known in human anatomy as the main branch of the facial) has 
a much greater extension, the result of the migration of the muscles 
from the hyoid region to their definitive position. 
The geniculate ganglion belongs to the visceral sensory system, 
the fibres of which run in the hyoid and palatine nerves to reach the 
sense organs in the oral cavity and in the spiracular gill when this is 
present. In those fishes where there are taste, organs on the outer 
surface of the body there is a ‘nerve of Weber’ (ramus lateralis ac- 
cessorius) which goes to the dorsal surface of the head and then to back, 
fins and tail, wherever the gustatory organs occur. It is frequently 
accompanied by fibres of the tenth nerve. In the mammals the visce- 
ral sensory fibres occur in the main trunk of the seventh, in the great 
superficial petrosal and in the chorda tympani nerves. This last is a 
post-trematic nerve which passes through the middle ear and thence on 
the medial side of the lower jaw to join the lingualis. 
In the adult anura and in the amniotes, where gills and lateral line 
organs are lacking, the facialis undergoes a corresponding reduction, 
