40 Journal of Comparative Netjkology. 



the olfactory areas. The epistriatum forms the dorsal half 

 of the wall of the fore brain, extending from the thalamus 

 immediately in front of and below the ganglia habenulae for- 

 ward above the lateral cavities to the olfactory commissure. It 

 is in direct connection ventrally with the striatum behind the 

 lateral cavities (Fig. 18) and laterally with the dorsal wall of the 

 olfactory area and lobe above these cavities. Thus, the striatum 

 and epistriatum are continuous only at the caudal end of the 

 fore brain. The shoving backward of the olfactory lobes and 

 areas which resulted in the formation of a Y-shaped cavity has 

 resulted also in splitting the striatum and epistriatum apart in 

 their cephalic portion. 



The cells of the epistriatum are arranged in two to four 

 rows adjoining the cavity. The larger end of the pyramidal 

 cell body is next the cavity and a large dendrite which arises 

 from the apex divides into two or more large branches which 

 expand in the fiber layer. The dendrites bear numerous small 

 spines which are knobbed at the end (Fig. 26) in the manner 

 characteristic of the epistriatum, inferior lobes, and tectum of 

 Acipenser. These peculiar spines are found nowhere in the 

 brain of Petromyzon except on the epistriatum cells. These 

 cells are so closely similar to the epistriatum cells of Acipenser 

 that it would be impossible to mistake their identity. The neu- 

 rites form a diffuse bundle which descends through the lateral 

 wall and end in the striatum proper (Figs. 18, 30). These 

 fibers are to be compared with the short neurites of the epistri- 

 atum cells in Acipenser. The epistriatum is traversed by a 

 large tract of fibers from the olfactory area, the tractus olfacto- 

 habenularis (Figs. 17, 17 a, 18). The tract is divided into many 

 bundles by the dendrites of the epistriatum cells, the largest 

 bundle running along the dorsal border of the epistriatum. At 

 its cephaHc end, near the olfactory commissure, fibers enter the 

 epistriatum from the cephalic wall of the olfactory lobe. These 

 are neurites of cells in the olfactory lobe which stand in connec- 

 tion with olfactory fibers in the glomeruli, i. e., part of the 

 olfactory tract. They come chiefly or wholly from the lobe of 

 the opposite side through the olfactory commissure and end in 



