CELL MASSES IN THE FOREBRAIN 425 
area with its several nuclei, is attested at once by the distribution 
of the fibers of the cerebral peduncle or internal capsule. This 
great bundle, where it is about to pass from the brain stem to the 
hemisphere (fig. 33), is bounded laterally by the optic tract and 
dorsally by the stria medullaris and stria terminalis. Medial 
and medio-ventral to this bundle is a large area of fibers which 
contains (1) the olfactory projection tract of Cajal (’04, fig. 778) 
descending from the olfactory portion of the amygdaloid complex, 
and (2) the medial forebrain bundle which follows the crus into 
the hemisphere and runs forward in relation to the tuberculum, 
caudate and other olfactory nuclei. 
The great lateral forebrain bundle or crus is composed of two 
parts, dorsal and ventral. The dorsal part is coarse-fibered and 
well medullated. It comes from the nucleus rotundus and ad- 
jacent cell masses in the dorsal part of the thalamus which 
correspond to the thalamic sensory nuclei in mammals. The 
ventral part consists of finer fibers which are well medullated at 
least in their course through the thalamus and corpus striatum. 
This bundle bends somewhat ventrad and runs caudad on the 
ventro-lateral surface of the thalamus and mid-brain until some 
distance behind the third nerve where it becomes more diffuse 
and seems to end at least in large part before the isthmus is 
reached. Without going further into descriptive details it is 
evident that the dorsal bundle contains the sensory radiations 
from the thalamus to the hemisphere and that the ventral 
bundle corresponds at least roughly to the efferent tracts from 
the hemisphere as we know them in mammals. 
These two bundles behave differently in the hemisphere. The 
dorsal deeper bundle bends up rapidly in larger and smaller 
fascicles through the lateral part of the striatum and enters the 
core of the dorsal ventricular ridge. The fascicles spread rather 
wide apart as they pass through the striatum but are all deep 
beneath the surface of the brain. Upon reaching the ventricular 
ridge the fibers enter into the formation of a uniform lace-work 
in the meshes of which the cells of the core-nucleus are evenly 
scattered. From this lace-work many fibers proceed into the 
dorsal pallum. This is the appearance seen in Cajal prep- 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, NO. 5 
