274 



NERVOUS SYSTEM OF VERTEBRATES. 



than the olfactory tracts which have long been known. The 

 olfactory tracts in fishes come to the hypothalamus either isolated 

 or mingled with the tractus strio-thalamicus. On account of 

 the latter fact the view has been advocated by some that a part of 

 the olfactor}' impulses were delivered to nuclei in the thalamus 

 proper. This is probably incorrect. When the medial olfacto- 



Fig. 136. — Scheme of the connections of the mammillary tracts, the nucleus 

 habenulae, and the nucleus dorsalis thalami. From Cajal (Textura, etc.). A, 

 corpus mammillare; B, nucleus dorsalis thalami; C, upper part of this nucleus; 

 D, nucleus habenulae; E, corpus interpedunculare; F, dorsal nucleus of the 

 tegmentum; /, optic chiasma; a, aqueduct of Sylvius; b, commissura habenularis; 

 c, commissura posterior; d, tractus habenulo-peduncularis; e, peduncle of the 

 corpus mammillare; /, bundle of Vicq d' Azyr; g, tractus mammillo-peduncularis; 

 /j, olf actor}' tract of projection (tractus olfacto-hypothalamicus) ; f, stria thalami 

 (tractus olfacto-habenularis) ; ni, thalamo-cortical fibers; n, cortico-thalamic fibers; 

 o, p, fibers of the stria thalami which cross in the habenular commissure. 



hypothalamic tract is mingled with the tractus strio-thalamicus 

 there are always many fibers going ventrally from the latter tract 

 into the inferior lobes and it is wholly probable that all olfactory 

 impulses enter the hypothalamus (except those to the nucleus 

 habenulae, see below). The tertiary gustatory tracts also enter 



