236 RALPH EDWARD SHELDON 
C. Judson Herrick traces the gustatory fibers of the fourth 
order into the caudal portion of the inferior lobes; it is likewise 
probable that tactile and other general sensory fibers reach the 
dorsal thalamic region through the medial lemniscus fibers. It 
is, therefore, probable, as Johnston and Herrick have already 
pointed out, that the ascending fibers from the pars dorsalis of 
the thalamus and from the hypothalamus are in the nature of 
general somatic and visceral sensory forebrain connections, respec- 
tively. The relations of the nucleus posterior tuberis need to be 
better understood, however, before the function of this ascending 
tract can be stated positively. It may be a connection for the 
transmission of visceral and somatic sensory impulses to the olfac- 
tory bulbs through the tractus olfactorius ascendens. 
Association connections 
Cajal and Golgi preparations show that practically all parts of 
the brain are permeated by a closely meshed reticulum of fine 
fibers, the ‘Punktsubstanz’ or formatio reticularis. In certain 
preparations it is almost impossible to identify individual cells, 
so close is the fibrous mesh. All parts of closely related regions, 
such as the different nuclei of the corpus precommissurale, are 
also placed in relation by means of large numbers of short con- 
nections. The same holds true with respect to regions derived 
from, the same morphological structure. This explains the con- 
nections between the nucleus intermedius and the nucleus post- 
habenularis, both of which are probably parts of the same dorsal 
olfactory column. It was noted earlier how the nucleus medianus 
separatesinto dorsal and ventral columns; how the dorsal continues 
caudo-laterad as the nucleus supracommissuralis, nucleus inter- 
medius, nucleus posthabenularis and habenulae; and how the 
ventral continues as the pars commissuralis, nucleus medianus 
and the nucleus preopticus. It is, therefore, to be expected, after 
what has been said regarding the close connection of associated 
regions that these two dorsal and ventral columns would possess 
short association connections. Such is the case and, while these 
fibers have been given the name of tracts, they are really all a 
