THE OSTEOLOGY OF VULPES MACKOTIS. 401 



Firm osseous union has solidly sealed together the various bones bounding the 

 auditory chamber, as the periotic, the squamosal (above), the tympanic, and the 

 auditory bulla (beneath), while to the inner side we see the bast- and exoccipital. 

 The sutures among the squamosal, parietal, alisphenoid, and frontal bones upon 

 the lateral aspect of the skull, remain clearly defined for the greater part of the 

 animal's life, and it is only in Canidse of extreme old age that they become to some 

 degree faintly defined or almost obliterated. 



Passing to the consideration of the base of the skull in Vulpes macrotis it is 

 interesting in the first place to note the extent of difference existing between it and 

 a skull of V. velox seen upon the same view, PI. XXII, figs. 5 and 6. Upon 

 examination of material in the United States National Museum it would appear 

 that these differences are constant and diagnostic. Principally, there are three of 

 them that are evident upon casual observation : — In V. macrotis the osseous palate 

 is transversely much narrower than in V. velox. This is especially noticeable 

 in the distance between the carnassial and first molar teeth of the opposite sides. 

 The malar portion of the zygomatic arch is deeper in the antero-posterior direction 

 in macrotis than in velox. The auditory bullce are comparatively larger in the 

 first-named fox than in the last-named. This character is very evident when we 

 come to compare series of skulls of these two well-marked species. In general the 

 entire skull of V. macrotis is thinner and more delicately fashioned than in velox, 

 and its being narrower throughout is easily appreciated upon comparison, either 

 from a dorsal or ventral aspect, PI. XXII, figs. 2, 5, 6 and 7. 



In the bony roof of the mouth in the specimen of V. macrotis at hand, the 

 sutures defining the limits of the premaxillary, maxillary and palatine bones have 

 become almost entirely obliterated. This is not usual in other Canidae, unless age 

 has very far advanced. We know, however, that in this family the suture between 

 the maxillaries and premaxillaries in this situation is a transverse one, extending 

 from a mid-point upon one canine tooth to pass directly across to the one upon the 

 other side, — the two, long, slit-like anterior palatine foramina lying partly upon 

 the maxillary side of the boundary, PL XXII, fig. 5. Otherwise, upon either side, 

 the maxillary supports the dental armature of the upper jaw in this, as in other 

 true foxes, namely, the four premolars, and the two true molars, each premaxillary 

 supporting three inciser teeth. Posteriorly, the free margins of the palatines are 

 rounded, forming, as they do, the anterior border of the posterior narial aperature. 

 Upon either side, the palatine bones are continued backward by the thin and com- 

 pressed pterygoid bones, which here, as vertical plates, descend directly downward 

 from the alisphenoids, terminating below in free laminae of bone, each known as the 

 hamular process of the pterygoid. Each is represented by a thin triangular plate 

 of bone in a vertical longitudinal plane, separated by an interval of nearly a centi- 

 meter in width. The valley thus created is deep and of some length (2 cms.), it 

 being the backward extension of the narial passage, and forms in the Canidae a 

 conspicuous feature of the mid-basal area of the skull. Above, either pterygoid 

 articulates with the under surface of the presphenoid and the basi-sphenoid bones. 



51 JOURST. A. N. S. PHILA., VOL. XI. 



