258 C. JUDSON HERRICK 



the pars dorsalis hypothalami and the nucleus of the tuberculum 

 posterius. 



Studies of the course of this tract in larval and adult Ambly- 

 stoma support this conclusion. Here I have seen collaterals 

 from these fibers both before and after their decussation ending 

 among dendrites of the pars ventralis thalami in a dense neu- 

 ropil. Dendrites from the pars dorsalis hypothalami and from 

 the nucleus of the tuberculum posterius are similarly related 

 to these fibers. 



The caudal end of the pars ventralis thalami and the pars 

 dorsalis hypothalami appear to be the chief places where this 

 tract terminates. We therefore term it provisionally the 

 tractus tecto-thalamicus et hypothalamicus cruciatus posterior, 

 though some of its fibers reach farther back to terminate in the 

 cerebral peduncle also. This tract evidently is not related to 

 the optic part of the tectum (colliculus superior) but only to 

 the part of the tectum which corresponds with the mammalian 

 colliculus inferior. 



I conclude that the tractus tecto-thalamicus et hypothal- 

 amicus cruciatus is a complex system, within which I have 

 recognized two chief subdivisions related respectively with the 

 urodele equivalents of the mammalian superior and inferior 

 coUiculi. These are termed the anterior and posterior parts 

 of the system. Each of these parts distributes its fibers diffusely 

 to the pars ventralis thalami, to the lateral parts of the hypothal- 

 amus, and to the nucleus of the tuberculum posterius in the 

 cerebral peduncle. The anterior part of this system in Nec- 

 tiu*us contains very few myelinated fibers and a much larger 

 number of unmyelinated fibers. The myelinated fibers after 

 decussation reach the lateral parts of the hypothalamus and 

 adjacent motor tegmentum. The unmyelinated fibers cannot 

 be so easily followed; they appear to be distributed after decus- 

 sation in part to the pars optica thalami, and in part to regions 

 farther ventrally. The posterior, or nonoptic part, is derived 

 from the colliculus inferior and contains numerous myelinated 

 and unmyelinated fibers which connect, both before and after de- 

 cussation, with the pars ventralis thalami, and after decussation 



