The Brain of Diemydylus Viridesceyis 261 



the geminums and a fragment of the cerebrum to illus- 

 trate histological structure. Burckhardt (6) in compar- 

 ing the brain of Ichthyophis with Triton, bases his main con- 

 clusions upon the European forms of triton, but records a few 

 observations upon the American form, diemyctylus. His 

 adult material was hardened and decalcified in a mixture of 

 chromic and nitric acids and cut through the entire head. 

 His general conclusion with regard to the urodeles may be 

 summarized as follows (p. 400) : They are uniform in the 

 non-existence of a neck-flexure, and in having a small pons- 

 flexure. The mesencephal appears like the myel in section. 

 The diencephal loses its connection with the epiphysis which 

 becomes functionless. The olfactory lobes are not distinct 

 from the cerebrum and the latter has no temporal lobe. The 

 double root of the olfactory nerve he considers of small phy- 

 logenetic moment. He considers that in this group a reci- 

 procity exists between the size of the united rhinen- and pros- 

 encephal and the united dien- and mesencephal. In the only 

 specific references to diemyctylus (p. 372), he says that the 

 two former equal in volume the two latter, that the mesence- 

 phal swells out into two corpora bigemina, and that, as in all 

 tritons, the mesencephal has a sulcus dorsalis (p. 377). 

 With regard to the general statements given above the obser- 

 vations in this article in the main agree. Neither of these 

 authors have touched upon the problem stated above, and 

 a number of matters are described and illustrated in this 

 article which have hitherto not been recorded. 



A preliminary paper containing some of the points here 

 given was presented at the American Association for the 

 Advancement of Science (18). 



BRAIN OF THE ADULT. PL. II-V. 



In general outline and proportion of parts the brain of die- 

 myctylus differs little from the other urodeles as shown 

 by Osborn and others. The united hemicerebrums and olfac- 

 tory lobes form the most conspicuous part of the brain and 

 overlap the diencephal which with the mesencephal forms 

 a rounded body. This in turn overlaps the metencephal, 



