182 A MANUAL OF ANATOMY. 



angle lies the portion of the cortex which is external to 

 the corpus striatum. As growth proceeds and the 

 cortex above and below overlaps more and more the 

 central depressed portion, the fissure assumes a linear 

 appearance. 



This is the horizontal limb of the adult fissure. About 

 the fifth month an offset from the main fissure appears ; this 

 ultimately becomes the vertical limb of the adult fissure. 



In the adult the fissure of Sylvius begins at the base of 

 the brain at the outer part of a perforated layer (anterior 

 perforated space), passes outward, backward, and slightly 

 upward until near its terminus, when it turns abruptly up- 

 ward to end in the parietal lobe. This is the main, or 

 horizontal limb of the fissure. Fig. 24. 



From the anterior part of the horizontal limb a short (one 

 inch long) fissure extends forward and upward into the 

 frontal lobe ; this is the ascending or vertical limb of the 

 fissure of Sylvius. Sometimes this fissure is bifid and one 

 part extends directly forward for a short distance into the 

 frontal lobe, forming the anterior limb of the fissure of 

 Sylvius. 



The fissure of Sylvius serves to separate the frontal and 

 parietal lobes above from the temporal lobe below. 



The Fissure of Rolando. Figs. I, 7, 23, 24, 26. 



This fissure appears between the fifth and sixth months of 

 fcetal development. It belongs to the class of fissures which 

 are formed by the heaping up of the cortical portion of 

 the cerebrum itself. It is found grooving the outer surface 

 of the cerebrum about at its middle. Its course is down- 

 ward and forward from about the middle of the great lon- 

 gitudinal fissure, into which it frequently opens, to near 

 the horizontal limb of the fissure of Sylvius. It forms an 



