66 THE MAMMALIA OF THE DEEP KIVER BEDS. 



close behind the orbits. The cerebral fossa is not only narrow, therefore, but it is 

 short, extending only slightly above the cerebellar fossa, and the lengthening of the 

 basicranial axis more particularly affects the floor of the latter. In the fossil which 

 is under description, the roof of the brain-case and the occiput, together with the 

 condyles, have been weathered away, and therefore the conformation of the sagittal 

 and occipital crests cannot be determined with certainty; but, from the character of 

 the frontal ridges and the shape of the cranial cast, which is well preserved, there can 

 be little doubt that these crests were very much as in Temnocyon coryphceus, to the 

 skull of which species that of Cynodesmus bears a very close resemblance. 



The upper contour of the skull is nearly straight and the descent at the forehead 

 very slight and gradual, in which respect we find a great similarity in shape to the 

 fox's skull. The basioccipital (so much of it as is preserved) is narrower than in 

 Canis, broader and more flattened than in Temnocyon ; in the latter, this bone is 

 anteriorly much narrowed by the extremely large bullae, and posteriorly displays a 

 median longitudinal convexity, with a deep fossa on each side of it. In the species 

 before us, the paroccipital process is very different from that of Canis ; in the latter 

 it is "long and prominent, and its anterior surface is applied closely to the back part 

 of the bulla, but to a less extent than in the cats, as the process is more compressed. 

 The mastoid is distinct but slightly developed" (Flower, No. 14, p. 24). In Cyno- 

 desmus, as in Temnocyon, the paroccipital process is much longer, more compressed, 

 and more curved downward and backward ; its free portion is much more widely sep- 

 arated from the bulla, with which the process is connected by a narrow bridge of 

 bone, which expands anteriorly so that the contact surface between the two is 

 about as in the existing genus. The mastoid is somewhat more exposed on the sur- 

 face of the cranium than in Canis and is more lateral in position, the paroccipital 

 processes occupying the inferior angles of the occiput. This displaces the mastoid 

 processes anteriorly, so that, as in Temnocyon, they are on the sides of the skull and 

 overlapped by the squamosal ; they are somewhat more developed than in Canis. 

 The tj'mpanics are inflated into large auditory bullae, which equal in actual size, and 

 therefore proportionally exceed, those of Canis latrans, though they are much less 

 prominent than in Temnocyon corypliaius. So far as can be judged from the speci- 

 men, the bulla appears to be divided by a septum, in very much the same manner as 

 in Canis, into two widely communicating chambers, of which the postero-internal is 

 much the larger. The meatus auditorius is an irregularly oval opening, which does 

 not form a tube; the anterior lip is, however, extended outward more than in Canis 

 and, separated only by a narrow slit from the post glenoid process of the squamosal, 

 articulates with it at its extremity. The shape and development of the bulla produce 



