84 Journal of Comparative Neurology. 



line of attachment of roof. 



The attachment of the roof is largely influenced by the 

 changes which take place in the margins of the rhomboidal 

 fossa. 



As has been shown by His, the neural tube is divided into 

 four longitudinal laminae, two dorsal and two ventral (Fliigel- 

 platte and Grundplatte). 



These laminae are well marked in the spinal cord and me- 

 dulla at early stages. The two dorsal laminae are connected by 

 the roof plate and the ventral laminae by the floor plate. 



The oblongata is characterized by the separation of the 

 dorsal laminae and consequent widening of the roof plate. 

 Fig. I. 



This separation begins at the calamus region and is most 

 marked at this region of the auditory vesicle and the interval 

 then decreases rapidly and the laminae meet again caudad to the 

 isthmus where they form the proton or fundament of the cere- 

 bellum (His). 



In human embryos of the fifth week, ten millimeters long, 

 according to His, a marked folding of the dorsal margins of the 

 dorsal laminae occurs. 



This takes place throughout the whole length of the rhom- 

 boidal fossae and the attachment of the roof is thus further 

 shifted laterad. In a few days this fold fuses to the outer sur- 

 face of the dorsal laminae, at the same time its margin of at- 

 tachment to the roof becomes drawn out into another fold or 

 lip which tapers into the epithelium of the roof His calls the 

 first fold the Rautenlippe and the second the secondary Rauten- 

 lippe ; as anglicized by Minot the rhomboidal lip and the sec- 

 ondary rhomboidal lip. Fig. i. 



Hitherto the primary rhomboidal lip has not been demon- 

 strated in the lower mammalia. 



Evidences of it appear in several rather advanced embryos 

 I have studied, namely, in the pig, sheep, cat and rat, as a 

 rounding of the dorsal margin of the dorsal lamina and an ap- 

 parent shifting of the roof attachment which does not proceed 



