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 VHIth nerve 

 has a very short course, breaking up on the under surface of the auditory sac to supply 

 at least three special sensory areas (ncu, PL VI. figs. 3, 4, 9, 10) in the otocystic 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 Hoffman (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). 6 F 



