258 THE BRAIN OF THE TIGER SALAMANDER 



the neuropil. Wliether any of them cross in the habenular commissure 

 has not been determined. A few of these fibers are myehnated. 



3. Tractus olfacto-habenularis anterior, ventral division. 



4. Tractus olfacto-habenularis anterior, dorsal division. 



As shown in figure 85, these fibers arise chiefly in the medial sector 

 of the nucleus olfactorius anterior, from which they diverge ventrally 

 and dorsally in a medial fascicle of fibers, which I have called the 

 "f. postolfactorius" (fig. 100; '27, p. 283, figs. 2-4). The fibers of this 

 system which are directed ventrally (no. 3) arise also in the ventral 

 sector of the anterior nucleus and the septum. They take a postero- 

 lateral course along the ventral surface of the hemisphere, turning 

 dorsally at the level of the anterior commissure to enter the stria 

 medullaris under the posterior pole of the hemisphere ('27, p. 284 and 

 figs. 5-17, tr.ol.hah.ant.). In the stria they lie anteriorly of the tr. 

 olfacto-habenularis (1 and 2) and posteriorly of the tr. cortico- 

 habenularis lateralis (5), as shown in sagittal sections (figs. 75, 76, 77, 

 tr.ol.h.a.v.). In the horizontal sections (figs. 25-34) this tract is 

 marked ir.ol.h.a. Some of these fibers terminate in the habenular 

 neuropil, and some cross at the posterior end of the habenular com- 

 missure in the com. superior telencephali. 



The dorsal fibers of this system (no. 4) cross from the medial to the 

 lateral side of the hemisphere in the f. postolfactorius between the 

 olfactory bulb and the anterior olfactory nucleus (fig. 5) and then 

 turn posteroventrally across the lateral aspect of the hemisphere in 

 company with the large tr. olfactorius dorsolateralis ('27, p. 284). 

 Over the piriform area these fibers are joined by those of tr. cortico- 

 habenularis lateralis (no. 5), and the mixed fascicle enters the stria 

 medullaris under the posterior pole of the hemisphere. In the stria 

 the mixed fascicle 4 + 5 ascends anteriorly of no. 3, and at the 

 boundary between ventral and dorsal habenular nuclei it splits into 

 lateral and medial bundles. The lateral fibers are dispersed in the 

 habenular neuropil, and the medial fibers decussate in the com. 

 superior telencephali (figs. 74-77, tr.c.h.l.). This component is shown 

 in horizontal sections in figures 30-34, and its entire course is seen in 

 transverse sections in figures 6-17 of 1927 {tr.c.hah.L). 



The anterior olfacto-habenular tract is the first component of the 

 stria medullaris to mature in ontogeny, its fibers appearing in early 

 swimming stages ('38, pp. 222, 238, figs. 10, 19); and its relations in 

 cyclostomes indicate that it is very ancient phylogenetically ('336, 



