260 THE BRAIN OF THE TIGER SALAMANDER 



7. Tractus septo-habenularis. These fibers arise from the septal 

 area and the bed-nuclei of the anterior commissure and ascend to the 

 stria medullaris between this commissure and the interventricular 

 foramen (fig. 75) . They spread in the ventral habenular neuropil and 

 have not been followed farther. In some preparations there is evi- 

 dence that these fibers are accompanied by others from the antero- 

 ventral part of the corpus striatum complex (primordial nucleus 

 caudatus) — a strio-habenular connection. 



8. Tractus cortico-habenularis medialis (figs. 32, 33, 34, 71, 76; 

 '27, figs. 11-17, here marked, str.med.). This is a large component of 

 unmyelinated fibers and a few thick fibers with myelin sheaths. They 

 arise from all parts of the primordium hippocampi, leaving its pos- 

 teroventral border in company with similar fibers of the hippocampal 

 commissure and tr. cortico-thalamicus medialis. Under the stem- 

 hemisphere fissure they turn sharply dorsad, to ascend as the most 

 anterior component of the stria medullaris. They spread widely in 

 the habenular neuropil, and some of them decussate at the anterior 

 end of the habenular commissure, thus forming the com. pallii 

 posterior. 



9. Tractus cortico-thalamicus medialis (figs. 31, 32, 72, 75). These 

 fibers are regarded as primordia of the columna fornicis. They ac- 

 company the tr. cortico-habenularis medialis, and some of their 

 fibers are collaterals from that tract and the hippocampal commis- 

 sure. They cross the stria medullaris obliquely and are not integral 

 parts of it except for the collateral connection mentioned. 



10. Tractus olfacto-thalamicus. This name was given to a col- 

 lateral connection from the stria medullaris to the neuropil of Bel- 

 lonci in Necturus ('336, p. 205). It is present also in Amblystoma. 



11. Tractus thalamo-habenularis. These fibers arising from the 

 dorsal thalamus and regions posteriorly of it enter the stria medul- 

 laris within the ventral habenular nucleus (fig. 76).. They are accom- 

 panied by fibers passing in the reverse direction, the tr. habenulo- 

 thalamicus ('396, p. 539; '42, p. 261 and fig. 77). This connection has 

 been described in mammals by several authors, recently by Marburg 

 ('44, p. 220) in man, where its fibers arise from the anterior nucleus 

 and pulvinar. 



The tr. strio-habenularis is probably present in Amblystoma but 

 has not been clearly seen. If so, its fibers may accompany those of the 

 tr. amygdalo-habenularis and tr. septo-habenularis, as mentioned 

 above. The former of these probable striatal connections is compa- 



