104 Journal of Comparative Neurology 



bryo almost without any cavities. The pia separates it from 

 the infundibulum and also sends wrapping membranes around 

 its various coils. I could find no evidence of penetration of its 

 folds by the dura. 



The Sulcus of Monro. — Reichert (69) first described this 

 sulcus in the human brain, where it extends from the porta to 

 the mesencephal and is called aulix by Wilder. Its morphological 

 importance is now recognized as it is the accepted boundary be- 

 tween the dorsal and ventral zones of His. In the turtle it is 

 clearly shown extending from the porta ventrad of the medi- 

 comissure to the cephalic part of the mesoccele where it disap- 

 pears (Figs 6 and 7.) I have not been able to detect sulci ceph- 

 alad of the metencephal that have any apparent morphologi- 

 cal significance. Sulci similar to those elsewhere described as 

 secondary are numerous in many portions of the brain. 



The Prosoplexus. — In the discussion of the roof of the dien- 

 cephal attention was called to the fact that the plexus in the 

 diaccele and about the region of the portas was derived from the 

 prosencephalic roof cephalad of the paraphysis. To this plexus 

 as a whole the term prosoplexus has been given. It is subdi- 

 vided into different parts according to the region in which the 

 parts occur and the usual names have been given to each. The 

 plexuses of the Amphibia have been worked out very complete- 

 ly by Mrs. Gage (30) and also by Mr. P. A. Fish in a paper 

 now preparing. These authors agree that a large plexus is de- 

 veloped immediately caudad of the paraphysis from the velum- 

 transversum of authors. This plexus hangs down into the dia- 

 ccele and extends caudad into the mesoccele. To this plexus 

 they apply the name of diaplexus. Cephalad of the paraphysis 

 another plexus (prosoplexus) is formed whose branches form 

 the various plexuses of the region of the portas and para- 

 coeles. In the turtle only this latter plexus is represented, no 

 plexus being developed from the velum. Cephalad of the para- 

 physis the plexus drops down into the aula forming the auli- 

 and paraplexuses. From this region it extends into the para- 

 coele to a distance varying in different individuals, sometimes 

 reaching to the rhinocceles. From the aula a part drops down 



