1884.] NATURAL SCIENCES OP PHILADELPHIA. 263 



mental ^ parts are clearlj^ differentiated from each other in 

 regular succession, beginning with the olfactory lobes or Rhinen- 

 cephalon, the Prosencephalon, the Diencephalon, the Mesen- 

 cephalon, the Epencephalon and Metencephalon. This was 

 not found to be the case in Amphiuma, where the Rhinen- and 

 Prosencephala and Dien- and Mesencephala are barely distin- 

 guishable. The exception above noted is that, the epiphysis 

 does not appear upon the external surface, but, as we shall see, is 

 altogether wanting, while a vascular plexus lying between the 

 hemispheres offers a very deceptive imitation of this important 

 structure. The hypophysis and infundibulum, however, have a 

 striking development. 



A careful study of the surface of the diencephalon discloses 

 a minute transparent area lying between two whitish streaks. 

 The latter are transverse commissures in the roof of the third 

 ventricle ; the former is the cavity of the epiphysial tube, or 

 recessus pinealis, the brain-cavity being separated from the pia 

 mater only by a single layer of cells. This transparent area has 

 already been pointed out by Goette^ in the frog, where it is 

 somewhat less conspicuous. In front of the foremost commissure 

 is a triangular transparent space ; at the sides of this are two horn- 

 like forward continuations of the diencephalon. These processes 

 I consider homologous with the habenulae of the mammalian 

 brain, and with the " Schnabelformiger Fortsatz " described by 

 Muller in the lamprey's brain. In the lamprey they coalesce in 



^ The nomenclature proposed by Prof. Burt G. "Wilder has been adopted, 

 with few exceptions. It proceeds upon the consistent plan of naming the 

 segments, and then- various parts, as far as possible, after the segmental 

 names which now meet with general acceptance among anatomists ; also of 

 using abbreviated forms of the longer terms now in use. For the sake of 

 clearness the new terms, and their synonyms, which are employed in this 

 paper are given below. The Prosencephalon, including: the procoilim, lateral 

 ventricles ; the proj)lexi, lateral plexuses ; the prosoccelia, ventriculus com- 

 munis laborum ; the supraplexus, plexus in the roof of the prosocoelia ; the 

 porta, foramen of Munro ; the terma, lamina terminalis ; the prcecommis- 

 sura, anterior commissure. The Diencephalon, including : the supra- 

 commissura, commissura habenarum ; the processus and recessvs pinealis, 

 the postcommissura, posterior commissure ; the diacodia, third ventricle. 

 The Mesencephalon, including : the mesoccelia, iter, etc. A system of this 

 kind must undergo modification, from time to time, but in the end it will 

 be far superior to the present cumbersome multinomial system. 



^ Entwickelungsgeschichte der Unke, 1875. 



