Blake, Roof of the Fourth Ventricle, 8i 



brains. By histological methods he found it absent in the dog 

 and cat, and concluded that its apparent presence in all animals 

 is due to a poor state of preservation of the brain. Also by 

 histological methods he finds that the lateral recesses are closed 

 in the lower animals. 



In regard to the appearance of the metapore, we find that 

 the usual description is that it is a perforation in the roof of 

 ventricle at the region of the calamus, varying in size and with 

 more or less ragged edges. 



Henle, Schwalbe and Key and Retzius describe its margins 

 as smooth or rounded, and the latter give its dimensions and 

 boundaries. Hoffman and Rauber describe it as appearing like 

 a short tube and not as a break in a membrane. 



C. S. Minot has suggested that it might be the orifice of 

 an evagination of the endyma. But as to whether he thinks 

 the orifice normal or artificial is not stated. 



The condition of these openings found in pathological 

 states of the brain vesicles, as hydrocephalus, cysts, etc., is of 

 interest as bearing upon their function and their necessity. The 

 evidence thus obtained, it must be confessed, is fragmental and 

 inconclusive largely on account of the lax methods and observa- 

 tions employed in autopsies. 



Absence of the metapore has been reported by O' Carroll 

 in two cases of hydrocephalus, by Neurath in another, and A. 

 Henle attributes hydrocephalus largely to the closure of the 

 ventricular openings. Sutton states that early closure gives 

 rise to ventriculo-meningocele and later closure to localized cysts. 



Hydrocephalus is also attributed to the presence of tumors, 

 especially in the regions of the mid- or hind-brain. 



Magendie has reported two cases of closure and concomi- 

 tant hydrocephalus in old people ; Martin St. Ange one in an 

 8-year old child ; Virchow a case of closure of lateral recesses 

 with localized cysts. The metapore has been reported open by 

 Morton in seven cases of tubercular meningitis, even where the 

 pia was much thickened. The efficacy of lumbar puncture in 

 hydrocephalus is admitted by many (A. Broca, P. Mau- 

 brac, Quincke, Jacobi), and Quincke has withdrawn lOO cc. of 



