235 



In a second contribution ^) the same authors designate the same 

 tract as "tractus taeniae" in Chimaera, and in Galeus show a tract arising 

 ventrally between the olfactory bulbs and curving dorsad around the 

 rostral end of the brain. This tract in Galeus is also called "tractus 

 taeniae". Referring to Kappers' earlier description of the brain of 

 Galeus ^), the only tract figured which niay correspond to the tract 

 here called "tractus taenia" is described under the name tractus me- 

 dianus, which runs caudally beneath the ventricle and joins the tractus 

 strio-thalaraicus. The tractus taeniae is correctly represented in the 

 same figures as running caudad in the ventro-lateral wall and rising 

 toward the nucleus habenulae. Apparently Kappees has greatly modi- 

 fied his original description of the forebrain of Galeus for the sake 

 of bringing it into agreement with his findings in Chimaera. His de- 

 scription of Chimaera, we shall see at once, is wrong, his earlier de- 

 scription of Galeus is nearer right. 



In the brain of Chimaera I have traced the two tracts in question 

 by means of Weigeet sections and have drawn a large number of 

 figures to demonstrate their course. The tractus pallii of Kappees 

 runs from the roof of the enlarged anterior portion of the telencepha- 

 lon caudad along the dorso-lateral surface until it reaches the region 

 of the optic chiasma when it descends gradually and enters the post- 

 optic decussation. This tract is clearly the same in essential respects 

 as the crossed tractus pallii in selachians and there is no disagree- 

 ment concerning it. The tract which courses along the taenia is cor- 

 rectly described by Kappers in the anterior part of its course. As 

 the accompanying Figs. 2, 3 and 4 show, its fibers in part end in the 

 medial wall of the lateral ventricle rostral to the unpaired ventricle 

 and in part traverse this wall to reach the rostro-ventral wall in the 

 region traversed by the anterior decussation. The tract rises in the 

 medial wall and runs caudad near the taenia (Figs. 5 and following). 

 But when it reaches the region of the optic chiasma instead of rising 

 to the nucleus habenulae, this tract takes a position on the lateral 

 surface above the tractus pallii, descends gradually with the latter 

 and then passes on into the hypothalamus (Figs. 15 to 26). (The 

 two tracts are so large and so sharply outlined that they can be fol- 

 lowed with the aid of a good hand lens.) This is therefore a tract 



1) Kappers, C. U. Ariens und W. F. Theunissen, Die Phylogenese 

 des Rhinencephalons, des Corpus striatum und der Vorderhirn-Kommis- 

 snren. Folia Neuro-Biologica, Vol. 1, No. 2, 1908. 



2) Kappers, The Structure of the Teleostean and Selachian Brain. 

 Journ. Comp. Neuro, and Psych., Vol. 16, 1906. 



