THE BRAIN AND SPINAL COED. 217 



that some of them are post-mortem products, for Hochstetter 

 found that when the brain of a 3rd month foetus, which had 

 been just removed from the mother, was hardened in situ, these 



fronto-par. oper. 



post. limb. fis. syl. 



temp. op. 

 island 



temp. oper. 

 island 



Flo. 1T9A.— The more common Condition of the Island of Eeil in Anthropoids. 

 Fro. 1795. — The complete isolation of the Island of Reil, the condition seen con- 

 stantly in the Human Brain and occasionally in the Anthropoid. 



temporary fissures were absent. But to this there are at least 

 two exceptions. 



(1) The choroid fissure caused by the ingrowth of the velum 

 interpositum and choroid plexus (Fig. 170). 



(2) The arcuate fissure on the mesial aspect, which has been 

 already described (Fig. 171). The hippocampal fissure, the 

 callosal, and probably the calcarine too, are remnants of this 

 fissure. 



The Sylvian depression is also visible from the second month 

 onwards, but it is in no sense a fissure comparable either to the 

 temporary or even to the permanent. 



The Fissures of the Brain. — The Principal Fissures of the 

 Brain include: (1) The Sylvian, (2) the Calcarine, (3) the 

 Hippocampal, (4) the 1st Temporal or Parallel, (5) the Parieto- 

 occipital, (6) Eolandic, (7) the Intra-parietal, (8) the Inferior 

 Pre-central, (9) the Collateral, (10) the Calloso-marginal. These, 

 with the exception of the first three (which have been already 

 described), appear at the commencement of the 6 th month. At 



