294 Wortman — Studies of Eocene Mammalia in the 



Creodonts ; it has a similar position in Oxycena and Patriofelis, 

 and probably also in Hycenodon, but of this latter genus I can- 

 not speak with certainty. In the marsupial skull its opening 

 is upon the under and more or less anterior surface of the bone, 

 as it is in Carnassidents. The paroccipital process is rather 

 small and has more of a backward and outward than downward 

 direction. Between the mastoid and exoccipital there is a deep 

 fissure, which at its upper extremity is pierced by a foramen, 

 as in the dog. 



Upon the under surface of the skull, Plate IV, the basiocci- 

 pital is rather narrow and the point at which it articulates with 

 the basisphenoid is much roughened for the attachment of the 

 recti capiti muscles. Immediately in advance of the condyles 

 is seen the single pair of large condyloid foramina. The tym- 

 panic bullae are of moderate size, rugose, and apparently devel- 

 oped exclusively from the tympanic, without inflation of any 

 part of the alisphenoid, as in the Marsupials. The external 

 auditory meatus is rather long and tubular and opens between 

 the mastoid and postglenoid. At the postero-internal angle of 

 the bulla is placed the irregular opening of the foramen 

 lacerum posterius, which is probably also the point of entrance 

 of the internal carotid artery, although I am unable to discover 

 any very distinct canal which answers to this foramen in the 

 carnassident skull. At the anterior extremity of the bulla are 

 the openings of the foramen lacerum medius and the eustachian 

 tube, and immediately in advance of these, on the prominent 

 ridge leading forward from the internal edge of the glenoid 

 cavity, are situated the foramen ovale and the posterior open- 

 ing of the alisphenoid canal. 



One of the most conspicuous features of the base of the skull 

 is the very large size and low position of the glenoid fossae ; 

 they are supported upon unusually thick, heavy processes of 

 the squamosals, which project much below the level of the base 

 of the skull. The cavity is relatively deep, and is spout-like 

 and transverse, the depth being considerably augmented by the 

 unusually prominent anterior and posterior glenoid processes. 

 The pterygoids are broad, thin, wing-like, and project consid- 

 erably below the base of the skull and the level of the palate. 

 The postnarial groove is continued well" forward ; it is deep, 

 rather narrow, but there is apparently no tendency for its 

 palatine boundaries to arch it over below, as in Hycenodon. 

 The optic foramina are distinct from each other and occupy 

 their usual position in the carnivorous skull, just in advance of 

 the sphenoidal fissure. In front of and a little above the optic, 

 near the junction of the frontal with the orbitosphenoid, is a 

 small but distinct opening which corresponds to the anterior 

 ethmoidal foramen of human anatomy, for the passage of the 



