400 Mr. A. Sanders. Anatomy of the [Mar. 9, 



II. " Contributions to the Anatomy of the Central Nervous 

 System in Vertebrate Animals. Sub-section I. Teleostei. 

 Appendix. On the Brain of the Mormyridse." By Alfred 

 Sanders, M.R.C.S. Communicated by [Professor Huxley, 

 LL.D., F.R.S. Received February 16, 1882. 



(Abstract.) 



The author, after a preliminary sketch of the literature of the sub- 

 ject, and a description of his method of hardening and staining, 

 proceeds to give an idea of the external aspect of the central nervous 

 system in the Mormyridae. 



Taking as an example the brain of the Hyperopisus dorsalis, he 

 describes it as comparable to that of an ordinary teleostean fish to 

 which two additions have been made, namely, an organ situated in the 

 region in front of the cerebellum, which grows out in the form of plates, 

 from a pair of stalks. These plates, or wings as they may be termed, 

 become folded in every direction, and breaking through the tecta lobi 

 optici, and repressing them to the base of the brain, they cover over 

 all the remaining lobes of that organ. 



It is only the tecfca lobi optici which undergo displacement, the tori 

 semicirculares retain nearly their usual position, so as to become 

 related to the former as an egg to the egg-cup, or an oyster to its 

 shell. 



On the outer side of the plates are minute ridges runniDg mostly 

 longitudinally, in close proximity to each other ; the parts where these 

 ridges become external are of a pinkish colour when fresh, but where 

 the plates are folded on themselves, the inner side of the wings 

 becomes external, and shows a white colour under the same circum- 

 stances. 



These folds take place when the plates have grown sufficiently to 

 reach the walls of the skulls, and are arranged as follows : — the plate 

 which grows towards the anterior end of the skull turns backwards ; 

 that which grows towards the summit of the skull turns inwards ; 

 that which grows outwards turns upwards, while that which grows 

 backwards ends in a free edge, and conceals the second of the addi- 

 tional parts alluded to above. 



This exists in the form of a large nearly spherical tuberosity placed 

 behind the cerebellum, in or over the region of the fourth ventricle. 



The author then gives an account of the microscopic anatomy of 

 this brain. Passing lightly over the remainder of the lobes, which 

 resemble in structure those of the ordinary teleostei, and noticing in 

 passing that the composition of the tecta lobi optici is much simplified, 

 he proceeds to describe the structure of the cerebellum. He finds that 



