Blake, Roof of the Fomth Venhicle. 105 



Furthermore, it leads to misconception and error. In a 

 recent text-book of anatomy, the author recognizing the neces- 

 sity of an actual demarcation between these so-called segments, 

 makes the statement that the third encephalic vesicle becomes 

 constricted transversely into the fourth and fifth and that a little 

 of this constriction remains in the adult. A misstatement hke 

 this certainly does not help a student to a true understanding 

 of this region. 



CONCLUSIONS. 



1. That compared with the lower mammals the rhom- 

 boidal lips reach a greater development in man. 



2. That consequently in man there is a greater develop- 

 ment of nervous matter in the roof of the fourth ventricle and 

 in the walls of the lateral recesses. 



3. That the disappearance of the walls of the lateral re- 

 cesses is of greater extent in the lower mammals. 



4. That in mammalia and aves a caudal protrusion of the 

 roof of the fourth ventricle is formed at some stage in their 

 embryonic life. 



5. That in mammalia there is a tendency to the ab- 

 sorption of the ventricular epithelium unless it is supported by 

 nervous matter or by the pia of neighboring structures. 



6. That in man the caudal protrusion becomes lost, giv- 

 ing rise to a metapore. 



7. That in all Anthropoidae there is generally a similar 

 metapore formation. 



8. That the Cercopithecidae represent an intermediate 

 stage between the Anthropoidae and the lower mammals, in 

 that there is a tendency to metapore formation. 



9. That in the lower mammalia the caudal protrusion as 

 a rule remains closed. 



10. That the lateral recesses represent an intermediate 

 area shared in equally by cerebellum and oblongata. 



11. To call attention to the presence in the human em- 

 bryo of a well-marked cavity between the protons of the vermis. 



12. That this cavity becomes obliterated by the fusion of 

 the opposing surfaces, and the tent is of later formation and 



