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Show 1892.] CEREBRAL HEMISPHERES OF RODENTS. 603 (on the right half), the Sylvian fissure also joins this longitudinally running furrow. A second longitudinal furrow, at about the same distance from the first described longitudinal furrow as the latter is from the median interhemispheral furrow, and commencing about 5 m m . from the posterior margin of the brain, has a course of 4 or 5 m m . ; this furrow is rather more strongly marked on the right half of the brain. Again, to the outside of this is a longer furrow but less strongly marked, which commences at the very margin of the brain just opposite to the point where the rhinal furrow is lost beneath the corpora quadrigemina; this furrow is situated about twice as far from the second longitudinal furrow as that furrow is from the first. Its length is about 12 m m . O n the under surface of the brain the hippocampal gyrus is seen to be very prominent in the temporal region, and when the brain is viewed laterally this convex projection is very apparent. The rhinal fissure is complete and anteriorly appears to give off a short forwardly running branch such as I have described in Ccelogenys. The Sylvian fissure is very slightly marked where it joins the rhinal fissure. The olfactory bulbs are large. Leuret and Gratiolet's figure (8, pi. iii.), though in m y opinion better than that of Owen, is not so clear as the drawing which I exhibit. Ccelogenys paca- Total length 53 mm., breadth 42 mm., height 23 m m . The cerebral hemispheres diverge posteriorly so as to display the corpora quadrigemina ; there is no divergence anteriorly. Each hemisphere measures 34 m m . in length and is considerably wider behind than in front, the diameter increases more rapidly after the Sylvian fissure. The surface of the hemispheres (fig. 4, p. 604) is indented by a few very deep furrows, which are quite symmetrically arranged. A furrow 10 m m . long lies posteriorly at a distance of 7 m m . from the interhemispheral sulcus ; anteriorly there is a shorter furrow which suddenly bends outwards posteriorly and runs almost parallel with the margin of the hemisphere. The posterior furrow is continued forward by a very faintly marked furrow which approaches the middle line and then turns outwards, joining or running just behind the end of the anterior furrow. On the right side of the body there is a small but deep indentation on the inner side of the posterior furrow, between it and the interhemispheral furrow; there is also (on both sides of the brain) another dint-it is hardly long enough to be called a furrow-on a level with the hind extremity of the posterior furrow and about as far from it as that furrow is from the median interhemispheral sulcus. Outside this again is a shallow furrow which begins at the posterior margin of the hemisphere, just on a level with the end of |