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Show 2/0 PROF. HUXLEY ON THE CRANIAL AND [Apr- $> I. Length of ^"- T Breadth ,, 7 Length of ^ - .... 3 Breadth ,, 3 Length of - , 13 ° m. 1 4 " m. 2 * * ' ' In the British-Museum specimen (No. II.) - is absent, and there is no trace of any alveolus for it. In absolute length, the skull No. I. (fig. 15, p. 268) comes very near C. cancrivorus (Table XIII. No. VI.), but differs from this in the relative length of the basicranial axis and shortness of the palate. It is a peculiarity of Icticyon which I have not observed in any other canine animal, that the upper and lateral margins of the occipital foramen are produced in such a manner as to give rise to a tubular prolongation which projects considerably beyond the occipital spine (fig. 15). Hence the total length given in Table XIV. is measured from the upper edge of this prolongation to the praemaxillary symphysis. The nasal bones are short and broad, and do not extend quite so far back as the fronto-maxillary suture. The glabellar region is evenly arched from side to side ; and the postorbital processes are but slightly prominent; Burmeister's figure, however, shows that these become larger with age. The frontal sinuses are but slightly developed backwards ; and this, judging by the marked constriction behind the postorbital processes in older skulls, appears to be the case even in old specimens. The skull figured presents a narrow sagittal area, and the sagittal crest is undeveloped ; but this feature also depends on the youth of the animal. In the large size of the paroccipital and mastoid processes, Icticyon resembles the larger Thooids of the Old World rather than its North-American congeners. The characters of the base of the skull are completely canine. The palate is wider in front than in G. cancrivorus. Posteriorly it is somewhat more prolonged and narrowed towards the nasal passage than usual; but a good deal of the peculiarity of appearance of this part of the skull of Icticyon arises from the small size of the hindermost molars. The tympanic bullae are not evenly arched as is usual in the smaller Thooids; but the outer is separated from the inner moiety of the convex surface by a well-defined oblique ridge. The rami of the mandibles are ankylosed together throughout the long symphysis, which measures 27 millims. This ankylosis has also taken place in the second specimen ; and I am not aware that it occurs in any other of the Canidae. The angle of the mandible is thick, short, and not produced inwards. Its lower edge is straight, and passes so abruptly into the convexity which follows, that the jaw presents, as it were, the next remove from the lobate condition beyond that of C. fulvipes (fig. 9, C, p. 252). II. 8 8 14*5 5 |