l88 yoiirtjal of Comparative Isleiirology and Psychology. 



Fig. S. Composite drawing of liorizontal sections tlirough the brain of a 

 tadpole of Rana catesbiana aboiit 30 niui. long, to show the central course of 

 the nervus terminalis. X '5^^- 



The specimen was beginning the metamorphosis when preserved, having 

 the hind k'g buds about (i mm. long. Sections wore cut in the horizontal plane 

 30 microns thick and stained with Delafield's hjematoxylin followed by 

 erythrosiu. In these sections the nuclei of the cells are clearly stained and 

 some of tlie forebi'ain tracts. Among the latter is the nervus terminalis on 

 both sides. Distally this nerve can be followed only a very short distance after 

 leaving the brain, its fibers being mingled with fila olfactoria and Indistin- 

 guishable from them, both being unmedullated. Centrally the nerve can be 

 followed back to the lamina terminalis, where it plainly decussates in tlif 

 anterior commissure. 



All of the details of this figure are taken from section 19 of the series, 

 except parts of the nervus terminalis which are taken from the neighboring 

 sections whose numbers they bear. Section 10 shows the nerve at its point of 

 entrance into the rostral end of the hemisphere and also its decussation in the 

 lamina terminalis. With the aid of the camera lucida I have projected upon 

 the outline of this section the remainder of the lutra-cerebral course of the 

 nerve, which is all included within the three sections lying next ventrad (sec- 

 tions 20, 21 and 22). Three elements of the anterior conunissure complex are 

 shown, the decussation of the nervus terminalis, the decussation of the lateral 

 forebrain bundle and the commissure of the corpora striata. The decussation 

 of the medial forebrain bundle lies in the plane of the section, but it is not 

 stained in the preparation ; cf. fig. 7. 



