CHAPTER VII 

 THE CENTRAL ACOUSTIC LOBE 



Having described the accessory organ of the herring we can now 

 turn to the consideration of the brain pattern of this fish, a typical 

 plankton feeder, and see whether it throws any light on the central 

 acoustic area we have described in the surface -feeding carps. The 

 medulla of a herring is much concentrated and has a well-marked 

 median lobe, projecting from the back of the cerebellum. This 

 lies in the position of the facial lobe of a carp, but microscopical 

 examination shows that it is connected with the acoustic tubercles 

 and has no anatomical relation with the facial nerve. When serial 

 sections are traced beginning at the hinder margin of this lobe, we 

 find that, resting on the fifth lobe, are two wings of tissue that meet 

 dorsally. These consist of groups of round cells between which 

 nerve fibres run, to meet at the apex, while an interrupted layer of 



round cells forms a cortex. As 

 the sections are followed for- 

 wards these wings become 

 thicker and finally have the 

 shape of a pear in section, 

 surrounded by a dorsal exten- 

 sion of the basal tissue, from 

 which it springs. 



Further forward the com- 

 mencement of the cerebellum 

 is seen lying dorsal to this 

 central lobe, and at the lateral 

 margins the acoustic tubercles 

 commence to make their ap- 

 pearance ; nerve fibres are seen 

 passing from these transversely 

 towards the central lobe. The 

 eighth or auchtory nerve is seen 

 entering laterally and forming 

 a distinct bundle of fibres 

 which approaches the central 



-Y(jo6e 



V. 



Fig. vi. 

 Section of Brain of Herring. 



-Lobe (somatic-sensory lobe). F.N. 

 Facial nerve. F.L. — Facial lobe. 



58 



