234 PROCEEDINGS OF THE ACADEMY OF [1889. 



now found separately in the various groups of carnivores, though 

 among the recent families the nearest approach to the primitive 

 condition is found in the dogs. The auditory bulla is almost cer- 

 tainly divided by a septum, as is still to some degree the case in 

 Canis, where the mode of development of the bulla is very like that 

 which occurs in the cats ; the alisphenoid canal and the post -glenoid 

 foramen are present ; the foramen lacerum posterius, carotid canal 

 and condylar foramen are all distinct from each other ; the mastoid 

 and paroccipital processes are free from the bulla? and are placed 

 far in front of the occipital condyles. It is usually taken for granted 

 that a short face is always a secondary modification, but the history 

 of several groups of mammals shows that this assumption is unten- 

 able in many cases. The primitive forms both of ungulates and 

 carnivores from the Puerco and Wasatch all have short faces, very 

 long and narrow crania, the orbits are placed far forward in the 

 face, and the zygomatic arches are in consequence greatly elongated. 

 The two factors which chiefly determine the modifications of the 

 skull are the teeth and brain, and the principles which Riitimeyer 

 has laid down with reference to the modifications of the ungulate 

 skull apply equally well to the carnivores. In the later forms the 

 orbit is shifted backwards and the zygomatic arches shortened, the 

 parietal zone reduced, the frontal zone extended, the teeth are much 

 enlarged and if their number is unreduced, the face becomes cor- 

 respondingly elongated, as in the dogs, or it may become greatly 

 shortened, accompanying the much reduced dentition, as in the cats. 

 Comparing the dogs of the White River, John Day and Loup Fork 

 epochs, the gradual elongation of the face becomes plain. 



The derivation of the Felicia' offers problems of much greater 

 difficulty than that of the other groups, and as we have already seen, 

 Schlosser altogether rejects the view that they have any connection 

 with the Viverridte, and derives them independently from creodonts. 

 According to Mivart the following characters are common to both 

 families and the hyenas. (No. 12, pp. 137-8). 

 " 1. Bulla greatly dilated, rounded, smooth, thin-walled, with one 



exception, osseous, and almost always divided by a septum 



into two distinct portions. 



2. Bony meatus short or with its inferior wall imperfectly ossified. 



3. Paroccipital process applied to and, as it were, spread over the 



hinder part of the bulla. 



4. Mastoid process never very salient, often obsolete. 



