506 'Journal of Comparative Neurology and Psychology. 



linie annehmen, so haben wir deren Ende am oberen Rande der 

 Lamina temiiualis zu siichen, vor der Stelle, wo die Fissura 

 chorioidea ihren Anfang nimmt." 



Now it must be noticed that more recent work (Piatt 1891, Hoff- 

 mann 1896, Neal 1898, and others) has shown that the entoderm 

 does not end anteriorly in contact with the Basilarleiste, but extends 

 forward beneath the terminal ridge. His did not study sufficiently 

 early stages to see this. Early stages show clearly that the basal axis 

 of the brain ends not in the Basilarleiste but in the terminal ridge 

 in which later the optic chiasma appears. Furthermore, this is 

 equally true of selachians, amphibians, birds and mammals. It is 

 altogether probable that the same is true of petromyzonts also, for 

 the depression called by Koltzoff "^infundibulum" is doubtless the 

 same as the primitive optic groove of other forms. In all vertebrates 

 studied by the writer the entoderm extends forward beneath the 

 transverse ridge which afterward becomes the optic chiasma. The 

 definition of the anterior end of the head previously given (Johnston, 

 1905) may now be simplified to read : in all vertebrates the anterior 

 end of the head is the point at ivhich the hrain plate meets the gen- 

 eral ectoderm at the same time that it comes into contact with the 

 anterior end of the entoderm. This point is marked in the adidt by 

 the optic chiasma. 



It has been shown in this paper that the depression in front of the 

 optic chiasma which has been known to His and other authors as the 

 recessus opticus, is related to the optic vesicles only secondarily and 

 is primarily a pit in the basal part of the neuropore (lamina termi- 

 nalis). 



2. The Hormology of the Saccus Vasculosus. — Here I wish only 

 to point out the homology of the saccus vasculosus of lower verte- 

 brates with the neural part of the pituitary body in man. The saccus 

 vasculosus is an evagination from the floor of the diencephalon which 

 is more or less branched, is lined by ependymal cells and sensory 

 cells, and is supplied by nen^e fibers ending in its epithelial lining. 

 In all lower forms it comes into close relations with the hypophysis. 

 In many cases the subdivisions of the two structures become inter- 

 mingled or interlaced. In man the neural part of the pituitary body 



