236 H. F. Osboin 



made for incomplete observation on the part of one or more observers. 

 There is still a strong general agreement. I think we may safely 

 homologize the olfactory tracts of the Teleosts with those of higher or- 

 ders, as Bellonci has done. The internal tract is homologous with a 

 corresponding bundle found in the Amphibia and Mammalia and repre- 

 sents an independent root of the olfactory nerve arising in the opposite 

 hemisphere. The external tract is a commissure homologous with that 

 part of the Pars olfactoria which is distributed to the olfactory lobes. It 

 is interesting to note that the olfactory tracts are quite distinct from the 

 hemispheral commissures, which is not the case in the higher orders. 

 The homology of the main commissures of the hemispheres is 

 more difficult because here the mantle is undeveloped. Rabl- 

 RücKHARD has compared these bundles with the pars temporalis. 

 By other authors they are described simply as the anterior commis- 

 sure. The question can, I believe, only be settled when we have a 

 knowledge of the Dipnoan brain which, according to Rabl-Rückhard, 

 approaches that of the Amphibia. At present I incline to the view that 

 we have here"a 'primitive form of the whole commissural system of the 

 hemispheres , thus equivalent to the upper and lower bundles in the 

 Amphibia. This is a much modified form of Miklucho-Maclay's ge- 

 neralization. For this, the term commissura interlobularis 

 (Göttsche), may be retained in preference to anterior commissure. 



Amphibia. 



In studying the Amphibian brain I have had the advantage of 

 procuring very extensive material including Menopoma^ Meno- 

 branchus, Axolotl, Amphiuma, Proteus, Salamandra, 

 R'ana mugiens and esculent a. The brain of the Urodeles is 

 throughout very much simpler than that of the Batrachia, but this is 

 especially true of the Perennibranchiates and Derotremata. 



In the stem of the hemispheres is a swelling of the floor which 

 is usually compared to the corpora striata. In the centre of this 

 swelling in Ran a is a group of cells which is entirely wanting in 

 Menobranchus and in the Derotremata so far as observed. In 

 the Urodeles the cerebral commissures traverse a ridge in the floor 

 of the large vcntriculus communis much as they do in the fishes. 



' According to Dr. .Jokdan of the Smithsonian Institution this is n sy- 

 nonyna of Cryi) tobranch us. 



