GADUS 75 



infundibulum, and is attached to the pituitary body and the 

 saccus vasculosus. The latter structure, which is of doubtful 

 significance, is peculiar to fish. It is a region of the brain- 

 floor where the wall is thin, thrown into folds, and very richly 

 supplied with blood-vessels. It has been supposed that its 

 function is to secrete the cerebro-spinal fluid which fills the 

 cavity of the brain and spinal cord, or to estimate the pressure 

 of this fluid. The olfactory lobes are peculiar in that they are 

 situated far forwards, close behind the nasal pits. They are 

 connected with the rest of the brain by long olfactory tracts. 



The olfactory nerves are short, which fact is correlated 

 with the length of the olfactory tracts. The optic nerves have 

 no chiasma. The three eye-muscle nerves, oculomotor, 

 trochlear, and abducens, are similar to those of the dogfish, 

 and call for no special comment. The profundus is reduced, 

 the trigeminal has the usual maxillary and mandibular branches. 



The facial nerve has ophthalmic, buccal, and hyomandibular 

 branches, innervating respectively the supraorbital, infra- 

 orbital, and hyomandibular lateral-line canals. In addition, 

 the facial nerve has a cutaneous branch which runs upwards 

 and backwards, and divides into three nerves which can be 

 seen immediately underneath the skin. One of these runs 

 along the base of the median dorsal fins ; another runs 

 obliquely down across the side of the body to the median 

 ventral or anal fin ; the last branch runs to the pectoral and 

 pelvic fins. 



The auditory nerve calls for no comment. The relations 

 of the glossopharyngeal and vagus nerves to the gill-slits is the 

 same as in the dogfish. The vagus supplies the heart and 

 viscera, and also the lateral line of the trunk. This nerve 

 supplying the lateral line branches, one portion remaining 

 close to the lateral-line canal, and the other runs a little below, 

 at the level of the septum which divides the myotomes into 

 dorsal and ventral portions. 



Sense-organs. — The nose is represented by paired nasal 

 sacs on the upper side of the snout, each with two openings, 

 and without connexion with the mouth. The eye is similar in 

 structure to that of the dogfish ; but there is in addition a 



