Herrick, Morphology of B7-ain of Bony Fishes. 67 



ventrad of this point the motor bundles of the peduncles gather 

 from the walls of the thalamus. 



The figures cited by Prof. Fritsch as the homolugues of the 

 " nucleus rotundus '" (Fig. XII, C, and Fig. XVl, E.), are cer- 

 tainly not to be so regarded, being, as correctly stated by Reiss- 

 ner himself, bundles of fibres. Furthermore, in both these 

 cases the position is too far cephalad, i. e., in the region of the 

 habena and anterior commissure(!) respectively, the actual homo- 

 logue, correctly described and located and well figured, was 

 overlooked, ( See Fritsch, Untersuchungen iiber den feineren 

 Bau des Fischgehirns, p. 59; Rf.issner, loc. cit., p. 90.) 



In the tailed amphibians there seems to be no very distinct 

 development of this nidulus, though we have examined sections 

 of Menopoma, Necturus, Salamander, etc., with reference to 

 this point. 



XI. — The nidulus siibt]iala)nicus is an irregular mass which 

 lies ventrad and cephalad of the nidulus ruber ( rotundus) and 

 adjoins the geniculatus cephalad. It is passed through by the 

 dorsal peduncular fibres, horizontal commissure tract, geniculate 

 tract and others in the most various directions, and is rich in 

 vessels. The microscopic structure consists in a vast number of 

 fusiform cells of small size and Deiters' granules. There are 

 very few of the large multipolar "switch-cells'" of the region of 

 the ruber. No strict homology with the nidulus subthalamicus 

 of mammals is intended, but this group includes all the gray 

 matter of the regio subthalamica, and may conveniently retain 

 that name. Embryonic material indicates the composition of 

 the cluster from various niduli. The whole subject of the gray 

 matter of the thalamus and mesencephalon requires subsequent 

 revision in the light of embryology.; 



DESCRIPTION OF PLATES. 



Fig. I. (In text.) Diagram of course of the various tracts in the mesen- 

 cephalic region. The brain is supposed to be viewed from above and the 

 parts are projected upon the horizontal plane. The ventral parts, except a 

 portion of the tuber cinereum, are removed. 



Plates A, B, and C of the special fasciculus issued in February con- 

 stitute Plates I, II and III of this volume. 



