No. 5.] HABENULAR TRACTS OF ACIPENSER. 229 



cells whose size and position I shall briefly indicate (Figs. 2-4). 

 First is the large dorsal and median portion bulging into the 

 central cavity and constituting about one-half of the entire 

 fore-brain. It is the corpus striatum. At the anterior end, 

 near the border of the olfactory lobe, are two compact groups 

 of cells, one ventral and median and one lateral, which together 

 make up the lobus postolfactorius. I shall refer to these nuclei 

 as the ventral and lateral nuclei postolfactorii (Fig. 2). Over 

 the greater part of the lateral surface of the fore-brain are 

 scattered small cells whose character I have not yet certainly 

 determined. I shall describe this area under the name of the 

 cortex (Fig. 3). The cells immediately surrounding the ventral 

 portion of the cavity of the fore-brain behind the anterior com- 

 missure together with those surrounding the recessus praeopti- 

 cus form a distinct nucleus which corresponds with the nucleus 

 thaeniae of Edinger ('96a). 



Three main fiber tracts are to be mentioned here (Figs. 

 2-4). The large number of fibers entering the fore-brain from 

 the olfactory lobe constitute a tractus olfactorius, although so 

 short as not to appear in the gross anatomy of the brain. 

 More conspicuous is the large bundle of fibers traversing the 

 ventro-lateral portion of each half of the fore-brain and enter- 

 ing the 'tween-brain, the tractus strio-thalamicus. A smaller 

 bundle connects the fore-brain with the Ganglion habenulae, 

 the tractus olfacto-habenularis. In addition to these longitu- 

 dinal tracts is the large anterior commissure connecting the 

 two halves of the fore-brain at about the middle of their 

 length. 



b. HISTOLOGY OF THE SEVERAL NUCLEI.-- (i) The corpus 

 striatum. The striatum contains two distinct types of cells 

 imperfectly separated into two nuclei. The internal (dorso- 

 median) nucleus (Figs. 2, 3, Epistriatum] is composed of pyram- 

 idal cells measuring 12 to 26 by 16 to 40 ^ arranged in 

 about ten to twelve compact layers parallel with the internal 

 surface of the striatum. The apices of the cells are directed 

 latero-ventrad. Each cell has several basal processes, and from 

 the apex arise from one to four dendrites which are marked by 

 characteristic spiny projections described by Van Gehuchten('94) 



