THE DORSAL SACK, THE AULIX AND THE DIEN- 

 CEPHALIC FLEXURE.^ 



B. G. Wilder. 

 Abstract. 



In many of the lower vertebrates there is a pouch-like 

 evagination of the diatela (membranous roof of the diacele, or 

 "third ventricle "j between the epiphysis and the paraphysis. 

 In Ceratodus and in Polyodon it is anteverted and very large. 

 In the green turtle it projects dorsad. Its mammalian repre- 

 sentative is crowded caudad by the cerebrum and rests upon the 

 retroverted epiphysis. It is commonly ignored in figures and 

 descriptions, but was shown by Reichert. The speaker, with- 

 out recognizing its homology, figured it in the Neio York Medi- 

 cal Journal, 1885, p. 320. It is large in the sheep and long in 

 the cow and horse. The diaplexuses are continued into it. 



Aiilix is the mononym proposed by the speaker in 1882 

 for the " Sulcus Monroi " of Reichert — a sigmoid groove on 

 the mesal surface of the thalamus just ventrad of the medicom- 

 missure and connecting the orifice of the mesocele with the 

 porta (foramen of Monro) at either side. His and C. S. Minot 

 regard it as the diencephalic representative of the '■' sidcus inter- 

 zonalis," the primary furrow between the dorsal and ventral 

 zones of the nervous axis. But recent observations in the 

 neurologic laboratory at Cornell upon embryo kittens render this 

 interpretation somewhat doubtful, and the matter is under inves- 

 tigation. 



In 1889, in the " Reference Hand-Book of the Medical 

 Sciences " the speaker called attention to the sharp angle be- 

 tween the prosencephalic and the diencephalic portions of the 

 brain cavities. A recent review of the brains of all vertebrate 



'Read before the American Neurological Association, June 4, 1896. 



