68 Journal of Comparative Neurology. 



PLATE IV. 



A series of horizontal sections through the ventral portion of the brain 



of Haploidonotus. All important structures were outlined with the camera 



lucida. 



Figs. I, 2. Sections through the hypophysis, tuber cinereum, and 



hypoaria. The decussation of the fibres of the epithelium of the hypo- 

 physis and the peduncle formed by similar fibres from the saccus are shown 

 in Fig. 2, which also passes through the tsase of the mammillare and 

 recessessus lateralis of the infundibulum. 



Fig. 3. The ventral peduncles are here in section and the tractus 

 tuberi ad commissuram ventralem is cephalo-mesad of it. 



Fig. 4 contains part of the ventral commissure and the small commis- 

 sura superior (uberi. Peculiar cell-less regions laterocephalad of the conus 

 prsecommissuralis is indicated as the postcinerea. 



Fig. 5 passes through most of the interoptic commissures. The tract 

 of the commissura horizontalis appears twice in the section. The medul- 

 lary part of the hypoarium we have termed nidulus niger, the cortical is a 

 cellulo-fibrous modification of the pes pedunculi. 



Fig. 6 occupies a position somewhat dorsad of Fig. 5 and passes 

 through the nidulus ruber (nucleus rotundus). The aubttialamicus lies 

 just cephalo-ventrad of the ruber. 



PLATE V. 



A series of horizontal sections of the brain of Haploidonotus farther 

 dorsad than those of Plate IV. 



Fig. I may *be compared with Plate XXV, Fig. 8, Vol. I, but it lies 

 somewhat dorsad. 



Fig. 2 lies somewhat ventrad of Fig. 2, Plate XXIV, Vol. I, and the 

 numerals refer to the same tracts to be discussed hereafter. 



Fig. 3 is a short distance dorsad of Fig. 3, Plate XXIV. In the latter 

 the reference numbers have the following signification: i.habena; 2, 

 cephalic optic tract; 3, Meynert's bundle; 4, posterior commissure; 5, 

 tract from commissura horizontalis and anterior peduncle of cerebellum , 

 6, cells giving rise to Mauthner's fibres; 7, lateral longitudinal fasciculus; 

 8, caudal brachium, etc.; 9, ganglion layer of the tectum; 10, caudal 

 optic tract ; 1 1, lemniscus ; 12, nidulus of cells in a dense stroma adjacent 

 to the lemniscus, 13, nidulus of fourth nerve. 



Fig. 4. A section somewhat ventrad of Fig. 3, Plate XXIV, Vol. I. 

 Attention is called to the so-called gelatinous tracts which pass from the 



