278 P. N. Bose—History of the Extinct Carnivora. 
the zygomatic process of the squamosal behind. In Hyenodon 
leptorhynchus (the only species of which the skull is well preserved) 
the malars are absent ; but they were evidently short, as inferred by 
De Blainville. In none of the Eocene Carnivores the angular 
process of the mandible is inflected inwards. In none the perforation 
of the lachrymal is upon, or external to, the anterior boundary of the 
orbit. The pterygoid processes are well developed, and generally 
considerably elongated posteriorly, especially in Cynodon (subgenus 
Cynodictis). In the Marsupials, on the other hand, these processes 
are invariably small and filiform. The form and arrangement of 
the facial bones too are generally very different from what obtains 
among the Didelphia. Even in Hyenodon, the constitution of the 
facial portion is such, that M. Filhol remarks, that ‘elle est absoln- 
ment différente, et ne me semble permettre aucune rapprochement 
entre le carnassiers phosphorites [Zyenodon] et celui d’Australie.” 
The humerus of Arctocyon is very stout and strong, with the 
deltoidean crest very largely developed, and indicates, as suggested 
by De Blainville, an animal which made great efforts with the 
anterior members either for digging or for swimming. It has been 
compared to the humerus of the Badger by De Blainville, and to that 
of Phascolomys by Gervais.” But if Arctocyon resembles this Mar- 
supial in the structure of the arm, the forearm of the former is very 
different. In the Didelphia the upper end of the radius is invariably 
small and rounded. But in Arctocyon, as well as in Hyenodon, 
Pterodon, Synoplotherium, ete., this part is broad and transverse, as 
in the normal Carnivora and Insectivora. The ulna of Arctocyon, 
thick, distinct, prolonged into a long olecranon, is very much like 
that of the Badger, except, perhaps, that the former was less 
apophysed than the latter. The humerus of Hyenodon, besides the 
great development and inferior prolongation of the deltoidean crest, 
is remarkable for the co-existence in it of a supracondylar and a 
large supratrochlear perforation, as in Mydans (one of the Suburside). 
The arm and forearm of Amphicyon have the strongest affinities with 
the corresponding bones of the Bear. In Cynodon too these bones 
are very much like those of the typical Carnivora. 
In the manus of the European genera, so far as known at present, 
the scaphoid and lunar were united, as in the typical Carnivora and 
some Insectivora. ‘The scapho-lunar of Amphicyon, described by De 
Blainville in 4. mayor, differs but slightly from the corresponding 
bone of the Bear. In a species of Pterodon in the collection of the 
British Museum I observed the coalesced seapho-lunar. In Cynodon 
too these bones are united. With regard to the American genera, we 
have no information concerning the scaphoid and lunar, except in 
the Synoplotheriwm of the Bridger formation, in which Prof. Cope 
says that these bones “appear to be distinct.” It would be, how- 
ever, too premature to generalize from this doubtful case of an 
extremely aberrant form even amongst the exceptional Carnivora, of 
the Eocene Period. With one or two probable exceptions, the manus 
was provided with five digits; and the movement was either quite 
1 op. cit. p. 190. * Nouy. Arch., etc. 1870. 
