DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 769 
It is difficult to follow the fibres of two nerves, so contiguous, to their centres in the 
brain; but fibres can be traced from the upper lateral edge of the medulla over 
a wide curve which brings them near the base of the third ventricle, or more correctly 
above the pyramids ; these must belong to the facialis ; and the auditory (VIII.) consists of 
those fibres which come out close to the surface of the medulla just below the overlapping 
posterior part of the optic lobe. These two nerves, in regard to their nuclei, thus are 
widely separated ; but where they arise from their common site on the upper margin of 
the medulla they are separable only by the fact that the fibres of the facialis pass down to 
the mandible and posterior margin of the hymandibular cartilage ; while the VIIIth nerve 
has a very short course, breaking up on the under surface of the auditory sac to supply 
at least three special sensory areas (neu, Pl. VI. figs. 3, 4, 9, 10) in the otocystie chamber, 
and forming a prominent ganglion outside the ear before doing so. Of the glosso- 
pharyngeal nothing can be said here, but the vagus (X.) apparently arises by two complex 
roots ; the first, which probably includes the fibres of the IXth nerve, issuing from a point 
near the lateral summit of the medulla oblongata, which point is in the same transverse 
plane as the oral termination of the notochord. It passes along the side of the medulla 
and penetrates the auditory cartilage, sending twigs apparently to the four gill-arches and 
to the pharynx. The nucleus of this portion of the vagus is confined to the superficial 
swelling of the lateral ridge of the medulla. Not so with the second part of the vagus. 
Its fibres describe an arch or curve, and can be traced to the median region of the medulla 
below the floor of the fourth ventricle and above the pyramids, while part of its fibres have 
a more superficial origin. On emerging they form a very massive, prominent root, passing 
in the main through the hind part of the ear-capsule, just above the thick basilar plate 
where it is in contact with the otocyst, and forming in front of the pectoral girdle a large 
double ganglion below and to some extent internal to the ear. The section which shows 
this bifid ganglionic mass presents another ganglion, apparently the ganglion of the first 
part of the complex. This ganglion is smaller, somewhat higher, and posterior to the 
large double ganglion. The former lies on the inner side of the anterior cardinal trunk, 
below which is a slender ganglion, whence twigs can be traced to the opercular region and 
to the skin, forming, between the muscle-plates and the neurodermis, a nervous tract, 
probably the origin of the lateral line. 
The large double ganglion first named lies just above and external to the pronephric 
swelling, the intimate relation of the two structures being noteworthy. Its fibres go, 
as before said, to the pharynx and the branchial arches, From the smaller ganglion, 
described above, pharyngeal and important cardiac branches also pass. 
Lateral Sense-Organs.—Little can be added to the observations of Horrman (No. 69) 
with reference to the development of the lateral sense-organs. In a young gurnard, 
about eight days old, they are very distinctly seen in the transparent though somewhat 
corrugated and glandular integument. Generally three or four can be made out in the 
haddock, one on the top of the head, just behind the eyes, a second situated a short distance 
behind the pectoral fin (see Pl. XVII. fig. 1), while one or two occur along the caudal trunk, 
VOL. XXXV. PART III, (NO. 19). 6F 
