SoRENSEN, Neurological Laboratory Notes. 5^ 



commissure, which Osborn calls the thalamencephalon. It is 

 obvious that the part of the brain since considered as dien- 

 cephalon in ganoids, and which I have called "Nebenhirn," or 

 parencephalon is not homologous with Osborn's thalamen- 

 cephalon, in the frog. In the frog larva there is a segment of 

 the brain roof between the post-commissure and the stalk of the 

 epiphysis." In another paragraph he states that these relations 

 are peculiar to Amphibia (p. 36.) " und eine vergleichende 

 Beleuchtung erfordern." 



Such a comparative study is now in progress and the fol- 

 lowing lines are intended to call attention to the topographical 

 relations in a few cases, with only incidental reference to the 

 morphological problems involved. In a median longitudinal 

 section of a duck embryo of six days the pineal appears as a 

 knob-like evagination from the median portion of the roof of the 

 diencephalon. Between ^ and ^ of the roof between the 

 pineal and mesencephalon is occupied by the post-commissure. 

 The remaining portion is precisely similar in structure to the 

 pre-pineal portion of the roof. The pre-pineal portion, i. e. , 

 the roof of the diencephalon from the pineal to the velum 

 transversum, describes a uniform convex curve, there being no 

 trace of supra-commissure, "polster, " dorsal sac, plexus, or 

 paraphysis. The pineal diverticle or recess exhibits the same 

 structure as the rest of the roof of the diencephalon, with, how- 

 ever, rather more numerous karyokinetic figures. 



In this stage the pineal is in almost immediate contact with 

 the epidermis. 



The dorsal roofs of the mesencephalon, diencephalon and 

 primary prosencephalon are approximately equal in extent 

 and lie in about the same straight line. The pituitary and 

 pharyngeal pouch are both lightly developed in this stage. The 

 former is closely approximated to the relatively large Infundi- 

 bulum (Hypencephalon). It therefore appears that the rela- 

 tions, which Kupffer claims are peculiar to Amphibia, are found 

 in the early embryo of the duck, and it becomes important to 

 trace the subsequent modifications. In embryos of the same 

 species, two or three days later, the relative position of the pin- 



