110 BRAIN AND BODY OF FISH 



the margin of the anterior nostril. These barbels have been des- 

 cribed as possessing taste-buds. 



The most important and unique characteristic of this fish is the 

 adaptation of the dorsal fin to subserve the function of taste. One 

 cannot do better than quote an early writer on this organ, for instance 

 Couch (1866) says, " the organ often represented as the first dorsal 

 fin lies in a chink from which it projects when the fish is in the water. 

 It is formed of a membrane from the edge of which rises a tliickly 

 placed row of threads, the foremost of which is the stoutest and 

 most prominent. This organ is in continuous and rapid motion. 

 It is well furnished with nerves which render it acutely sensible to 

 impressions." (It is now known to be well provided with taste- 

 buds.) " This dorsal organ is supphed by a special nerve which 

 reaches it directly from the brain, a branch of this nerve also goes- 

 to the pectoral and ventral fins which are thus endowed with 

 particular sensation (these are also provided with taste -buds), in 

 addition to those of action, the last-named faculty being controlled 

 by branches of the intercostal nerves." 



We quote the above as showing the accurate anatomical observa- 

 tions of the older authors. The following description of the brain of 

 a five-bearded rockling is from a specimen which had been specially 

 hardened for the purpose of cutting serial sections. 



We reproduce a drawing of the naked eye appearance (see 

 Plate 18, Fig. iv) of the brain after the cerebellum had been 

 removed to expose the medulla oblongata. The primitive end- 

 brain, as in the burbot, is large, approaching the optic lobes in 

 length. The optic lobes are of moderate size compared with 

 those of other gadidse. The acoustic tubercles are prominent 

 and prolonged posteriorly into the somewhat globular somatic- 

 sensory lobes. These are prolonged caudally by extensions 

 which would be similar to those of the burbot, if they were not 

 displaced and separated by the globular eminences of the enlarged 

 facial lobes, which meet but do not fuse in the middle line. The 

 vagal lobes are very prominent more caudally and join in the middle 

 line. 



The study of serial sections will show the dominance of the facial 

 lobe in the sensory elements of the medulla. We give a series of 

 sections of the medulla oblongata, which have been drawn under 

 low power by means of a projector apparatus (Plate 22). The first 

 drawing is a section of across the somatic-sensory lobes near the 

 base of the cerebellum, and it cuts across both the facial nerves which 

 have a transverse course just below the fifth lobes. These nerves 

 are remarkable for their size, no doubt due to the branches of the 



