660 THE NERVOUS SYSTEM. 
(3) the mandibular arch (inferior maxillary nerve). The mandibular is at first the main nerve ; 
and the maxillary division is sometimes regarded as a subordinate branch (prze-branchial, pre- 
trematic) for the supply of the anterior margin of the cleft (mouth), with which the nerve is in 
relation. The ophthalmic nerve is sometimes regarded as a morphologically separate nerve. 
The nerves to these arches have been compared to the anterior primary divisions of spinal 
nerves, the branches 
which they supply to 
the forehead and temple 
(frontal, orbital, and 
auriculo- temporal) re- 
presenting the posterior 
primary divisions. The 
ganglia on each division 
of the nerve are formed 
as extensions from the 
Gasserian ganglion. 
~lhe facial nerve is 
essentially the nerve of 
the second (hyoid) arch, 
and the cleft in front 
of that arch (spiracular 
cleft, Eustachian tube). 
Its motor root supplies 
| the muscles of that arch 
| (stapedius, stylo-hyoid, 
and digastric), and the 
epicranial and _ facial 
muscles and platysma 
myoides, which are de- 
velopments from the 
hyoid arch (Rabl). The 
chorda tympani nerve 
is regarded as the sub- 
ordinate (pree-branchial, 
pree-trematic) branch to 
supply the anterior 
margin of the first post- 
oral cleft. It is possible 
that the geniculate 
ganglion, with the pars 
intermedia and the 
chorda tympani may, in 
part at least, represent 
Fic. 473,—SCHEME TO ILLUSTRATE THE DISPOSITION OF THE Myoromes 1x the ganglionic and 
THE EMBRYO IN RELATION TO THE HEAD, TRUNK, AND LIMBS. afferent element of the 
A, B.C, First three cephalic myotomes; N, 1, 2, 3, 4, Last persisting cephalic reer Or the geniculate 
myotomes; OC, T, L, 8, Co, The myotomes of the cervical, thoracic, ganglion, and the nerves 
lumbar, sacral, and caudal regions ; I., II., III., IV., V., VI., VIL, VIII., 1 relation to 1t, may be 
IX., X., XI., XII., refer to the cranial nerves, and the structures with associated with an “ epi- 
which they may be embryologically associated. branchial” sense-organ. 
The auditory nerve, 
on the other hand, may be either the sensory element of the branchial nerve, associated with 
the hyoid arch and first post-oral cleft, or it may represent the nerve or nerves belonging to 
ancestral sense-organs of the lateral line. 
The glosso-pharyngeal is the branchial nerve of the third post-oral (thyro-hyoid) arch and 
the cleft in front. Its efferent fibres supply the muscle of this arch,—the stylo-pharyngeus. The 
superior constrictor of the pharynx is also assigned to this arch; the middle and inferior 
muscles to the fourth (first branchial) arch. The afferent part of the nerve is possibly composed 
of two elements; the petrous ganglion being associated with an epibranchial or lateral line 
sense-organ, and the rest of the nerve forming the afferent fibres for the gill-cleft and arch. 
The lingual branches are regarded as the main stem (post-trematic), the pharyngeal branches as 
subordinate branches ; the tympanic branch being the pre-branchial or pree-trematic branch for 
the anterior margin of the gill-cleft. 
The pneumogastric nerve is generally regarded as representing the fusion of all the branchial 
nerves behind the glosso-pharyngeal. Its efferent fibres are in series with those of the glosso- 
pharyngeal above and the spinal accessory nerve below, and belong to the lateral series of His. 
Its afferent fibres, like those of the glosso-pharyngeal, consist of two elements. The lower 
ganglion has possible connections with epibranchial sense-organs; the rest of the nerve repre- 
senting the fused branchial branches of fishes. The superior laryngeal nerve is looked upon 
as the branchial nerve of the fourth, and the inferior laryngeal nerve as the branchial nerve 
of the fifth arch. The auricular branch is sometimes, but erroneously, regarded as the homo- 
logue of one of the lateral nerves of fishes. While the relation of the nerve to the hinder gill 
