52 THE BRAIN OF THE TIGER SALAMANDER 



habenula is the f. retroflexus (chap, xviii), which terminates in the 

 cerebral peduncle and interpeduncular nucleus. In the brains of lower 

 vertebrates the habenular complex is one of the most widely spread 

 and physiologically important members of the central correlating 

 apparatus. Its primary function seems to be to integrate the activi- 

 ties of all parts of the brain that are under olfactory influence with 

 the exteroceptive functions of the tectum and thalamus in the inter- 

 est of higher cerebral control of the feeding reactions of the skeletal 

 muscles. 



13. HYPOTHALAMUS 



In the large preoptic nucleus and hypothalamus, olfactory connec- 

 tions dominate the picture, as they do in the habenular system; but 

 here the nonolfactory functions represented are interoceptive instead 

 of exteroceptive. All parts of the cerebral hemisphere are connected 

 with the hypothalamus by fibers passing in both directions in the 

 medial forebrain bundles (p. 273), stria terminalis (p. '^55), and 

 fornix (p. 254) systems. The visceral-gustatory afferent paths are 

 shown in figure 8. Large tracts from the thalamus and tectum also 

 end here, so that all kinds of sensory experience of which the animal 

 is capable are represented in the hypothalamus. This experience is 

 here organized in terms of visceral responses. The efferent tracts go 

 to the peduncle, tegmentum, interpeduncular nucleus, and descend- 

 ing fibers in the deep neuropil which are precursors of the f. longi- 

 tudinalis dorsalis of Schiitz. There is a large tract to the hypophysis 

 for nervous control of endocrine activity. There is also evidence that 

 some neuro-endocrine functions are performed in the hypothalamus 

 itself (Scharrer and Scharrer, '40). The structure of the hypothala- 

 mus has been described ('21a, '27. ''^5a, '36, '42, and in the embryologi- 

 cal papers, '37-'41). It is similar to that of Necturus, of which more 

 detailed descriptions have been published ('336, '346). For the com- 

 position of the postoptic commissure see chapter xxi. 



14. STRIO-AMYGDALOID COMPLEX 



The primordial corpus striatum occupies the thickened ventro- 

 lateral wall of the cerebral hemisphere and, like all the rest of the 

 hemisphere, is under olfactory influence. This is stronger at its an- 

 terior and posterior ends. Anteriorly, it is divided by a striatal sulcus 

 into dorsal and ventral parts (fig. 99), and posteriorly it is much en- 

 larged as the amygdala (figs. 1, 96, 97), which has the typical mam- 

 malian connections (fig. 19). 



