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Show 1892.] CEREBRAL HEMISPHERES OF RODENTS. 599 breadth until about the middle point, when the margins are nearly parallel, converging slightly posteriorly. The rhinal fissure is quite continuous; the Sylvian fissure is represented by the merest trace. O n the upper surface of the brain there are two short furrows on each side, one in front of and to the outside of the other. Lagostomus trichodactylus.-Total length 43 mm., breadth 35 mm., height 18 m m . The cerebral hemispheres diverge posteriorly so as to display the corpora quadrigemina ; they do not diverge at all anteriorly. The extreme length of each hemisphere is 31 m m . The hemispheres Fig. 2. W-\\ Brain of Lagostomus trichodactylus. A, from above; B, from tbe side: a, b, c, longitudinal fissures; S, Sylvian fissure. See p. 607. are wider behind than in front; the breadth increases very gradually up to the Sylvian fissure ; at this point the brain suddenly becomes wider. The brain (fig. 2) is marked by several fairly deep furrows and by other slighter ones. These are perfectly symmetrical. On either side of the intercerebral fissure is a furrow 9 m m . long which |
