| OCR Text |
Show 1899.] BRAIN OF HYDROCHffiRUS. 801 parts, an anterior shorter, and a posterior longer region. It is the fissure lettered a of m y former paper-the most prevailing fissure of the Rodent brain. In a second brain (fig. 2, p. 800) the fissure in question is also broken on the left side by a bridging convolution, in this case on the right side also, as is the case with the brain figured by Dareste. It will be noticed that this furrow posteriorly approaches the median furrow of the brain, that dividing the hemispheres, and is very nearly lost to sight over its edge. In the third brain (fig. 3) the furrow a is again broken on the left side, but complete upon the right. Furthermore the furrow (fig. 3) completely disappears from view posteriorly, and this region of the gyrus, which is bounded externally by the furrow in question, is very distinctly depressed below the general surface of the brain. Fig. 3. Cerebral hemispheres of Hydroch&rus, dorsal view. Nat. size. The conditions that have just been described seem to give a clue to the nature of this sulcus and gyrus. The lobus hippocampi narrowing as it passes backward turns up the back of the brain and becomes continuous with this gyrus, which I therefore consider to be the hippocampal gyrus appearing upon the dorsal surface of the brain. In this feature the brain of the Capybara resembles that of certain Carnivora1 and of certain Ungulata 2. The fissure which I letter b is, as in other Rodents, short; it is, however, quite deep and well-marked. It runs obliquely inwards in all three brains. i Helictis (Garrod, P. Z. S. 1879, p. 307); Gulo (Beddard, P. Z. p. 143), &c. &c. 2 Moschus (Flower, P. Z. S. 1875, p. 174); Dicotyles (Turner, Journ. Anat. 1891, p. 134), &c &c. |
