THE CORTICAL GRAY MATTER. 199 



(Zuckerkandl). The fascia dentata is of first importance accord- 

 ing to Alexander Hill. He calls attention to the fact that the 

 Narwhal, which has no sense of smell, possesses every part of 

 the hippocampal region excepting the dentate fascia (Campbell). 

 The imcus comprises the whole anterior part of the gyrus hippo- 

 campi. In structure the crown of the hippocampal gyrus and 

 the uncus are nearly identical. They have only five layers of 

 cells, (i) As already pointed out the plexiform layer is thick 

 and possesses a dense stratum zonale, only second to that of the 

 subiculum. (2) The place of the small pyramids is usurped by 

 the "olfactory islets" (Calleja) which are curious nests of large 

 stellate cells (28^) interspersed with small nests of very minute 

 pyramidal cells. (3) The tassel-cells of Cajal. Peculiar pyram- 

 idal cells, with such rich dendritic arborizations hanging from the 

 bases as to resemble tassels, are seen in the place of the medium- 

 sized pyramids. At the line of Baillarger there are no cells; the 

 fourth layer of typical cortex is entirely wanting. (4) The 

 stellate layer and internal layer of large pyramids are replaced 

 by a layer of intermixed fusiform and triangular cells heavy w r ith 

 Nissl bodies. (5) The fusiform-cell layer is nearly typical. 



Nucleus Amygdala (Fig. 32). In the anterior wall of the 

 inferior horn of the lateral ventricle, near the temporal pole and 

 dorsal to the uncus hippocampi, is the amygdala, a nucleus of 

 doubtful classification. The amygdala is in part continuous 

 with the corpus striatum and, according to Campbell, appears 

 on the surface of the uncus as the gyrus semilunaris. 



Cortex of the Lower Wall and Lip of the Hippocampal Fis- 

 sure (Fig. 62). This is known as the subiculum. It is especially 

 distinguished for its remarkable stratum zonale, which is visible 

 to the naked eye, and for its long radiations, which reach the 

 zonal layer and give the cortex a striated appearance, (i) The 

 plexiform layer is almost wholly occupied by the stratum zonale, 

 called here the external medullary lamina. (2) The layer of 

 olfactory islets. The islets are closely packed nests of minute 

 triangular cells, 5^ in diameter, resembling those in the uncus. 

 (3) The stratum radiatum occupies about three-fourths of the 

 depth of this cortex. In its deep part (the stratum lucidum) 



