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Show 1880.] DENTAL CHARACTERS OF THE CANIDAE. 245 the interorbital and the temporal regions of the skull. In Canis azaree the temporal ridge is not so well marked ; and, beginning to diverge from its fellow a little in front of the coronal suture, it passes with a very slight curve to the angle of the supraorbital process, while the postorbital constriction is small (fig. 1, A ) . Moreover there is hardly any depression on the upper surface of the supraorbital process, the whole glabellar region being evenly arched from side to side. In the Fox, there is a well-marked depression on the outer part of the upper surface of the supraorbital process, and the glabella is flatter. These external differences answer to small but very definite distinctions which are seen in the longitudinal sections. The superimposed sections of the two skulls correspond almost exactly. In C. vulpes, as in all the Canidae, the cribriform plate of the ethmoid bone is funnel-shaped, the concavity being turned towards the cranial cavity, while the convex surface looks outwards and upwards above, outwards and downwards below, into the nasal chamber. From its outer surface the delicate rolled laminae of bone which answer to the superior and middle turbinals of human anatomy take their origin. The lower plates project backwards as far as the ethmo-praesphenoidal suture ; while the upper ones reach as far back as the junction of the ethmoid with the frontal bones, and are covered over by the orbital and nasal prolongations of those bones. In C. vulpes, however, there are no frontal sinuses ; that is to say, behind the point of union with the ethmoid the median parts of the thin frontal bones are solid throughout. Moreover, if, as in man, we distinguish that part of the frontal bone which covers the anterior surface of the cerebral hemispheres, from that part which lies further back, as the forehead, then the forehead of the Fox is very short, while the vertical height of the ethmoid is proportionally great. In Canis azarce there is a marked difference in all these respects (fig. 4, A,/, p. 246). A large frontal sinus is developed in each frontal bone, above and behind the fronto-ethmoidal suture. The forehead is much longer, while the height of the ethmoid is less. In both skulls a well-defined ridge (fig. 4, a) answers to the supraorbital sulcus, and marks off the region occupied by the curved lateral gyri from that of the orbital and frontal gyri of the brain. But in the Fox this ridge (fig. 4, B, a) is directed upwards and forwards, and its dorsal end is separated by but a small distance from the dorsal margin of the cribriform plate of the ethmoid; while in Canis azaree the dorsal half of the ridge (fig. 4, A , a) is inclined slightly backwards, and its end is far more remote from the edge of the cribriform plate. Moreover the inner wall of the skull is much more sharply bent inwards along the dorsal half of the orbito-frontal ridge than it is in the Fox. These differences have their counterparts in the form of the brain, and become very manifest when casts of the interior of the skull are compared (fig. 5, p. 247). In the Fox the contour of the brain, viewed from above, is that of a pear with the narrow end forwards. Late- |
