CORRELATING CENTERS IN THE DIENCEPHALON. 



2 75 



the inferior lobes and both gustatory and olfactory tracts are 

 widely distributed in the hypothalamus. In higher vertebrates 

 nothing is known of the central gustatory tracts. The corpora 

 mammillaria have long been known as the place of ending of the 

 chief olfactory conduction path, the fornix. From the mam- 

 millary bodies the tractus mammillo-peduncularis goes caudally 

 and is comparable with the tractus mammillo-bulbaris in fishes. 

 Collateral branches from the fibers of this tract near their origin 

 form the tractus mammillo-thalamicus to the nucleus dorsalis 

 thalami (Fig. 136). The cephalic part of the hypothalamus, the 

 tuber cinereum, has never been well understood in mammals. 



Fig. 137. Sagittal section of the tuber cinereum of the newborn rat. From 

 Cajal (Textura, etc.). A, anterior or chief nucleus; B, posterior nucleus; C, internal 

 nucleus of the corpus mammillare; D, optic chiasma; E, afferent tract from the 

 forebrain (tractus olfacto-hypothalamicus) ; F, nucleus supraopticus; a and b, 

 branches of bifurcation, and d, terminal branches of the afferent fibers. 



The first important contribution toward a clear understanding of 

 its relations has been made recently by Cajal. This author shows 

 that the two nuclei of the tuber cinereum receive bundles of non- 

 myelinated and myelinated fibers which come from the septum 

 pellucidum of the cerebrum, run close over the optic chiasma 

 and end in these nuclei and in the mammillary bodies. These 

 tracts are illustrated in Figures 137, 138, taken from Cajal's text- 

 book. As the discussion in the next chapter will show, these 

 fibers are homologous with the medial olfacto-hypothalamic tract 



