140 BRAIN AND BODY OF FISH 



THE LOBI INFERIORES, SACCUS VASCULOSUS 

 AND INFUNDIBULUM 



There is an area of the brain that receives in teleostean fisli 

 even less consideration than the cerebelhim does in human anatomy 

 — we refer to the ventral surface of the brain which lies beneath 

 the optic lobes, posterior to the crossing of the optic nerves, and 

 anterior to the medulla oblongata. This area is illustrated in the 

 drawing of the brain of the halibut. In the right hand figure the 

 lobi inferiores appear partially obscuring the large optic lobes. 

 They are large bean-shaped bodies with their median surfaces in 

 apposition. In the middle line in front of these is the spherical 

 pituitary body. The apposition of the pituitary body and lobi 

 inferiores is not complete, and a triangular space is left, by which 

 there emerges, on the ventral surface of the brain, the red thin- 

 walled saccus vasculosus. 



Anterior to the lobi inferiores, the most prominent area of grey 

 matter is the lobus infundibuli. From the third ventricle, which 

 lies in front of the level of the optic lobes, there passes a hollow 

 passage in the body of the lobus infundibuli. This passage is 

 prolonged downwards and somewhat backwards and communicates 

 ventrally with the cavity of the pituitary body. Whereas the ven- 

 tricle is lined with ciliary epithelium the infundibulum has a lining 

 of ependyma, which in part consists of large multipolar nerve 

 cells. Before terminating in the cavity of the pituitary, that 

 is to say more dorsally, the infundibulum communicates with 

 large cavities within the lobi inferiores, and finally it is prolonged 

 into the saccus vasculosus ; this is a thin-walled glandular sac and 

 is very vascular ; its function would appear to supply the ventricles 

 with their fluid content. If the drawing of the transverse section 

 of the optic lobes of the plaice be referred to the saccus vasculus 

 will be seen and its communication with the infundibulum. 



The ventricles of the lobi inferiores are also to be seen, and dorsal 

 to them on either side are two very characteristic oval areas of 

 nerve cells, these are the nuclei rotundi. The minute anatomy of 

 these nuclei is as follows : a number of round or oval islets of grey 

 matter lie in a granular matrix interspersed with nerve fibres. 

 Nerve fibres pass from the ventral part of the lobi inferiores into 

 the nuclei and some smround it. Dorsally, a large strand of 

 nerve fibres passes from the nucleus to the thalamus. 



Before considering the very important subject of the pituitary 

 body, we propose to mention the relations of the lobus infundibuli 

 to the lobi inferiores. We have made a special study of the course 



