DIENCEPHALON 243 



hypothalamicus cruciatus (tr. tecto-hypothalamicus anterior) from 

 the superior colliciilus and {%) the posterior division of this tract from 

 both inferior and superior colhcuh (fig. l'^). 



Through these manifold afferent connections nervous impulses are 

 discharged into the hypothalamus from almost all parts of the brain, 

 directly or indirectly. All sensory systems are represented here, but 

 the olfactory connections evidently are preponderant. The signifi- 

 cance of this convergence will appear after comparison with similar 

 pools in the habenula and several other places (p. 252). 



INTRINSIC HYPOTHALAMIC CONNECTIONS 



All parts of the hypothalamus are interconnected by dense and 

 intricately woven neuropil in both gray and white substance. Though 

 all activities of the hypothalamus may thus be integrated, the struc- 

 ture is diversified, indicating the inception of specialization of the 

 local nuclei as these are seen in higher animals. The most complicated 

 and interesting of these local fields of neuropil surrounds and per- 

 meates the chiasma ridge, of which I have given a detailed descrip- 

 tion ('42, p. 214). Neuroblasts of this area are differentiated very 

 early in embryogenesis ('37, '38), and some of their axons form tr. 

 hypothalamo-peduncularis (figs. 18, 23) and tr. hypothalamo-teg- 

 mentalis (fig. 21), as elsewhere described ('42, p. 226). This area 

 seems to be the primary focus into which converge all tracts of the 

 ventral part of the hypothalamus for discharge through the two 

 tracts just mentioned. Among these afferents are the intrinsic fibers 

 of tr. preoptico-hypothalamicus from in front and of tr. infundibu- 

 laris ascendens from the postero ventral lobe. 



The last-mentioned ascending tract divides. One moiety is directed 

 dorsally, providing a broad connection from the ventral part of the 

 hypothalamus to the dorsal, and a larger moiety is directed forward 

 into the medial forebrain bundle. Most of these ascending fibers ap- 

 parently end in the postchiasmatic neuropil and preoptic nucleus, 

 but some may go farther into the hemisphere ('336, p. 250; '346). 

 This tract is quite independent of the ascending fibers of the olfactory 

 projection tract previously mentioned. There are probably other 

 fibers which ascend from the hypothalamus in the basal forebrain 

 bundles, but our preparations have not revealed them. 



From the anterior part of the ventral thalamus, fibers stream back- 

 ward into the dorsal part of the hypothalamus. These thalamo- 



