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Show 244 PROF. HUXLEY ON THE CRANIAL AND [Apr. 6, The premolar teeth are smaller in C. azarce; but as they are more worn it is difficult to make an exact comparison. The upper sectorial is not quite so long as that of the Fox. The transverse diameter is the same in front, but is less behind, in 0. azarce; and its inner cusp is less forward in position and less prominent. The lower sectorial is narrower and the anterior internal cusp somewhat larger in C. azaras. In both, a line drawn from the anterior-external to the anterior-internal cusp (a b, fig. 3, p. 243) makes an acute angle with a transverse line, on account of the not very backward position of the latter. In the Fox there is a very small secondary cusp between the inner anterior and the inner posterior cusps, which is absent in C. azarce. The second lower incisor lies completely behind the first in C. azarce ; but this is probably only an individual exaggeration of a tendency to the displacement of the second incisor backwards, which is often observable in the Canidae. TABLE II.-Measurements of the Cheek-teeth ofC. vulpes and C. azarae. C. vulpes. C. azarcB. Length of the whole upper prsemolar and molar series Length of the whole lower pr-semolar and molar series Length of ^ - m. 1 j> Breadth of -- Length of r^- : Breadth of - Length of -p^ **- m. 2 " mil In both C. vulpes and C. azarce the hinder ends of the nasal bones just reach the level of the hindermost part of the fronto-maxillary suture. In the Fox the ascending processes of the prae-maxillary bones reach the anterior processes of the frontal bones, while in C. azarce there is a wide interval between the two. In both, the temporal ridges unite into a crest for a short distance behind ; but for the rest of their extent they are separate, inclosing a very narrow sagittal area (fig. 1, p. 241). At the anterior extremity of this the ridges diverge and pass outwards to the angles of the supraorbital process; and it is at this point that the principal external difference between the two skulls becomes apparent. In the Fox (fig. 1, B, p. 241), the well-defined ridge runs nearly parallel with its fellow for some distance in front of the coronal suture, and then sweeps outwards, in a sharp curve, to the recurved supraorbital process, behind which a deep constriction marks the boundary between 54 50 60 13 9*3 11 5 7*3 15 7-3 3 57 12*5 9 11 5 7 14*3 '•5 3*5 |