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Show 266 PROF. HUXLEY ON THE CRANIAL AND [Apr- 6> Thus Q. caama, C. bengalensis, C. corsac, and C. velox appear to be mere local varieties of a small Alopecoid form answering pretty nearly to the Jackals in the Thooid series, and occupying the southernmost part of the Alopecoid zone, from South Africa to Central America. The more differentiated Alopecoids, though largely coexistent with these, are preponderant in the north of the zone. I can meet with no evidence of the existence of any true Alopecoid in South America, which appears to be the head quarters of the lower Thooids. Among these, C. vetulus has the least modified dentition, and in this respect corresponds with C. littoralis among the Foxes. This species is figured and fully described by Burmeister. The skull has a low median sagittal crest; and the ramus of the mandible is slender and nonlobate. In the one imperfect cranium which I have seen (from which the measurements in Table XIII. are given) the length of the sectorial and first molar in the upper jaw is the same, and does not exceed 17 per cent, of the basicranial axis. The length of the lower sectorial is rather less than 23 per cent. The crown of the upper sectorial or fourth premolar is broadly triangular (breadth in front 5*5 millims. to length 7 millims.), on account of the great size of its internal cusp, and resembles that of Otocyon. The inner anterior cusp of the lower sectorial is lower than the outer ; but a line drawn through both is almost transverse to the axis of the tooth, the heel of which is very stout. In Brazil, in Demerara, and in Guiana the canine animals which have been named Canis cancrivorus, C. fulvipes, C. brasiliensis, C. rudis, and that to which I have referred above as C. azarce (a) occur. The crania belonging to the first four which have come under my observation are, for the most part, rather larger than that of the last, have a less-marked subangular lobe and slightly larger sectorial teeth ; but there is no sharp line of demarcation between the two sets, and I regard them all as local varieties of C. cancrivorus. Moreover, in those forms, such as C. rudis, in which the skull is largest, the approximation to Canis azarce (the most widely distributed of the South-American Canidse) is so close, that I cannot separate the two by any osteological or dental characters. Canis magellanicus presents the same sort of relation to C. cancrivorus as G. simensis, in the Old World, bears to C. aureus and G. anthus. The size of the body, and notably of the jaws, has increased without any corresponding enlargement of the teeth (Table XIII.). In the large relative size of the upper molars, Canis jubatus adheres to the same type; while C. antarcticus, on the other hand, presents the closest approximation to some specimens of G. latrans (Table XIII.). From the range of variation of C. cancrivorus, it can hardly be doubted that the examination of more extensive materials will prove the existence of an uninterrupted series of gradations from G. vetulus to C. antarcticus and C. jubatus. Burmeister1 remarks that Canis cancrivorus, C. fulvicaudus, and C. vetulus are distinguished by the relative shortness of their jaws from C. azarce, C. griseus, and C. 1 Erlauterungen zur Fauna Brasiliens, p. 46. |
