270 PROF. HUXLEY ON THE CRANIAL AND [Apr. C, 



I. II. 



Length of"^ 7 8 



Breadth „ 7 8 



Length of — 3 



Breadth , 3 



Length of --J 13 14-5 



^2 4 5 



In the British-Museum specimen (No. II.) '^^ is absent, and 

 there is no trace of any alveohis for it. 



In absolute length, the skull No. I. (fig. 1.5, p. 268) comes very near 

 C. cancrivorus (Table XIII. No. VI.), but differs from this in the 

 relative length of the basicranial axis and shortness of the palate. 

 It is a peculiarity of Icticyon which I have not observed in any other 

 canine animal, that the upper and lateral margins of the occipital 

 foramen are produced in such a manner as to give rise to a tubular 

 prolongation which projects considerably beyond the occipital spine 

 (fig. 15). Hence the total length given in Table XIV. is measured 

 from the upper edge of this prolongation to the prsemaxillary sym- 

 physis. The nasal bones are short and broad, and do not extend quite 

 so far back as the fronto-maxillary suture. The glabellar region is 

 evenly arched froin side to side ; and the postorbital processes are but 

 slightly prominent ; Burmeister's figure, however, shows that these 

 become larger with age. The frontal sinuses are but slightly deve- 

 loped backwards ; and this, judging by the marked constriction behind 

 the postorbital processes in older skulls, appears to be the case even 

 in old specimens. 



The skull figured presents a narrow sagittal area, and the sagittal 

 crest is undeveloped ; but this feature also depends on the youth of 

 the animal. In the large size of the paroccipital and mastoid pro- 

 cesses, Icticyon resembles the larger Thooids of the Old World 

 rather than its North-American congeners. The characters of the 

 base of the skull are completely canine. The palate is wider in front 

 than in G. cancrivorus. Posteriorly it is somewhat more prolonged 

 and narrowed towards the nasal passage than usual ; but a good deal 

 of the peculiarity of appearance of this part of the skull of Icticyon 

 'arises from the small size of the hindermost molars. 



The tympanic bullae are not evenly arched as is usual in the 

 smaller Thooids ; but the outer is separated from the inner moiety 

 of the convex surface by a well-defined oblique ridge. The rami of 

 the mandibles are ankylosed together throughout the long symphysis, 

 which measures 27 millims. This ankylosis has also taken place in 

 the second specimen ; and I am not aware that it occurs in any other 

 of the Canidse. The angle of the mandible is thick, short, and not 

 produced inwards. Its lower edge is straight, and passes so abruptly 

 into the convexity which follows, that the jaw presents, as it were, 

 the next remove from the lobate condition beyond that of C./ulvipes 

 (fig. 9, C, p. 252). 



