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Show 450 DR. J. F. GEMMILL ON [Apr. 10, corresponding layer is non-pigmented, richly cellular, and becomes continuous with the brain-wall just in front of the optic recess, in such a way that the central cavity of the brain is prolonged into the space between the retina and the pigment-layer. An optic stalk, embryonic in condition, is thus present. Two deep grooves are found in the floor of the third ventricle and the mid-brain, each leading down into a separate infundibulum and hypophysis. The grooves are separated by a considerable ridge of brain-tissue. The right hypophysis and its hypoaria are somewhat compressed; the rest of the brain is normal. The right palato-quadrate bar is absent and the trabecular cranii are displaced to the left (fig. 1, PI. XXXIII.). Taken by itself, the supernumerary eye might seem to be simply a case of repetition, since its nerve is derived from the right optic nerve. But the persistence of an embryonic optic stalk, together with the presence of a double hypophysis in the brain, indicates rather that the explanation is to be found in an extremely local degree of axial duplicity which has become obscured by the growth of the predominant twin head. A. somewhat analogous case is described by Gurlt (' Lehrbuch der pathologischen Anatomie,' ii. Theil, p. 221 : Berlin, 1832). The right ramus of the lower jaw in a L a m b has an accessory ramus on its inner side with an accessory set of molar teeth. The tongue is double anteriorly. There are two pituitary glands and two infundibula arising from a single large tuber cinereum, two pineal glands, three pairs of corpora quadrigemina, and two aqueducts of Silvius. Three accessory nerves, arising from the mid-ventral line of the brain, go to an "ocular rudiment in the sphenoid." This account is quoted from Taruffi ('Storia della Teratologia,' vol. iii. p. 155). For other examples of duplicity of the hypophysis see Ahlfeld (' Die Miss-bildungender Menschen,' p. 73 : Leipzig, 1880) and Bland Sutton ('Transactions of the Odontological Society,' 1888). The second specimen was quite normal in appearance, except for the presence of a tiny refractive knob behind the left eye. Examination of serial sections showed the knob to contain a lens of considerable size, enveloped in muscle-fibre, but unaccompanied by any other eye-structure, lying in front of an exceedingly minute fore-brain and third ventricle. The cavity of this third ventricle communicates with the mid-brain cavity of the normal head (Plate XXXTII. fig. 2). The embryo was quite lively when obtained, and its chances of survival would probably not have been appreciably diminished by the small tumour in question. It will be seen from fig. 2 that the functional eyes and fore-brain belong to a predominant right twin head, as also do the olfactory organs, the mouth, and the anterior cranial cartilages generally. The back part of the brain and the whole of the body are, however, composite, since the left moiety of them represents structures which are continuous with the left side of the left (aborted) twin, while their right side is a continuation backwards of the |