CELL MASSES IN THE FOREBRAIN 419 
laris, the stria terminalis, fibers of the sensory radiations from 
the thalamus, an olfacto-hypothalamic projection tract, and an 
anterior commissure bundle. 
The simple enumeration of these tracts shows that while the 
amygdaloid complex in mammals is a compact collection of cell 
masses occupying a restricted area in the temporal pole, it is a 
complex of very diverse elements which have been brought 
together by mechanical forces and have no primary functional 
unity. 
The extent of the hippocampal formation. The morphological 
relations of the hippocampal formation have been treated with 
some fulness In a previous paper (’13b). There is now to be 
noticed the boundary between hippocampus and general pallium 
and the relation of the hippocampal formation to the amygdaloid 
complex. In the rostral part of the hemisphere the characters 
shown. in figure 47 enable us to fix the boundary of the hippo- 
campus with some degree of accuracy on the basis of cell arrange- 
ment. Above the fimbrio-dentate sulcus, which separates the 
homologue of the fascia dentata from the primordium hippo- 
campi and fimbria, there are first pyramidal cells compactly 
arranged in a ventricular layer with few peripheral cells. The 
cells are smaller than the cells in most parts of the general pallium 
but are neither so small nor so closely crowded as the cells in 
the deep layers in the middle part of the dorsal pallium in this 
region. ‘This is the portion which is now generally accepted as 
the homologue of the fascia dentata of mammals. There is no 
clear separation or distinction between fascia dentata and hippo- 
campus in this turtle’s brain. 
Dorsal to this, the cells in the medial wall are less closely 
arranged, appear larger and are less deeply stained. Many cells 
here are placed far from the ventricle, even lying in the outer 
half of the wall. Many cells adjacent to the ventricle are dis- 
tinctly pyramidal in form and have large, dominating apical 
dendrites. This loose arrangement of cells rather suddenly 
gives way to a compact arrangement near the dorso-medial 
angle of the hemisphere. The dorsal area of compact cells will 
