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Show 1891.] DOLICHOTIS P A T A G O N I C A . 243 the Sylvian fissure is very deep ; it passes forwards and then backwards, forming a line which is convex anteriorly ; after this it bends forwards at a sharp angle and nearly joins the principal longitudinal sulcus (see fig. 4). The upper surface of each cerebral hemisphere is marked by a strong sulcus running with a sinuous outline approximately parallel to the long axis of the brain ; these sulci commence a little way in front of the hinder margin of the Fig. 4. Brain of Bolichotis patagonica. A, from the side; B, from above : S, sylvian fissure; R, rhinal fissure. brain; anteriorly each bends outwards and joins the rhinal sulcus ; the other fissures are of less importance and are illustrated in the drawing exhibited (fig. 4). I have been able to compare the brain of this species with those of the following Rodents at present in m y possession :- Castor fiber (a cast of the brain * ), 1 For this and several other casts of the brain itself, not of the cranial cavity, I a m greatly indebted to Prof. d'Arcy Thompson. 16* |