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Show 294 MR. W. A. FORBES ON THE GREAT ANTEATER. [Mar. 7, above by a shallow fissure (a), which, at the level of the anterior extremity of the prominent" hippocampal lobe," turns downwards, and runs along the external and inferior face of that lobe till it terminates on its inner face (fig. 4, a), not, however, reaching the hippocampal sulcus (h). At the point where its downward course commences there is a small triangular area (I. s.s.) exposed on the lateral surface of the brain, from which a short curved shallow sulcus (s) runs a short way upwards, forming with the descending part of a a forwardly-convex curve. In the larger specimen figured (fig. 3) this short upwardly-running sulcus (s) is separated, as will be seen, by a narrow bridging fold from the triangular depression and its posterior continuation (a). From the antero-inferior angle of this triangular space, but separated by a very narrow, more or less deep, bridging convolution from a, another sinuous fissure (b) runs forwards and upwards to terminate near the anterior angle of the hemisphere l. Above, on the supero-lateral aspect of the brain, and nearly parallel with the median longitudinal fissure, is a distinct longitudinal sulcus (c), convex upwards, which runs in an antero-posterior direction for a space of 1*2 inch. Finally, parallel with the posterior edge of the hemisphere, dividing the external surface of this "temporal lobe," is a vertically-directed sulcus (d) about */5 inch in extent. On the internal aspect of the brain (fig. 4) runs a well-marked " calloso-marginal" sulcus (cm), broken up into three or more parts, the most posterior being nearly vertical in position, and separated by but a little space from the posterior extremity of fissure a. In its usual position is a well-marked hippocampal sulcus (h), with a broad "fascia dentata'''' between it and the corpus fimbria turn, the fascia dentata being continued, as described by Prof. Turner in Dasypus 2, as a thin layer of longitudinally-disposed fibres over the corpus callosum to near its genu. The hippocampal sulcus does not extend as high as the corpus callosum. The lateral ventricle is fair-sized : I can see not a trace of any posterior cornu. The hippocampus major is strongly convex. The "hippocampal lobe" has, on its interior aspect, a few irregular dentations developed near its antero-internal angle. In the smaller and simpler brain of Tamandua (represented dia-grammatically in fig. 5, p. 295), the only sulci present are those corresponding to a, b, c in the larger species, with some slight representatives of d. Adopting the late Prof. Broca's ideas 3 as to the nature and composition of the " scissure limbique," the inferior arc of this is clearly represented by the fissure a, which is separated by a narrow "pli de passage retro-limbique" (fig. 4, ?\/)from its superior arc, represented 1 In the smaller specimen (fig. 2), this fissure is, on the right-hand side only, broken up into two by a narrow bridging convolution ( + ). 2 Journ. Anat. Phys. i. p. 314 (1867). " Anatomie compared des circonvolutions cerebrales. Le grand lobe limbique et la scissure limbique dans la serie des Mammiferes," Revue d'Anthro-pologie, vii. pp. 385-498. |