440 Wortman — Studies of Eocene Mammalia in the 



to the fenestra ovalis from below may be taken as conclusive 

 evidence that the course of the entocarotid artery was essen- 

 tially different from that in the modern Insectivora. Just 

 external to the fenestra rotunda may be observed the periph- 

 eral termination of the fallopian aqueduct, through which 

 the facial nerve made its exit from the skull. In front of the 

 occipital condyle is placed the opening of the main condyloid 

 foramen, and at some little distance in advance of it is the 

 accessory or second condylar foramen — so constant a feature 

 of the Marsupial skull, and occasionally found among living 

 species of the Insectivora. Its office is apparently unknown. 

 Immediately posterior to the petrosal eminence is situated the 

 rather large elliptical opening of the foramen lacerum pos- 

 terius, the size of which, in connection with the almost 

 vestigial condition of the postglenoid foramen, would seem to 

 indicate that the chief venous channel through which the 

 cranial cavity was drained, made its exit at this point. A 

 broad, but distinct, groove internal to this foramen leads for- 

 ward to the fissure between the periotic and basioccipital, 

 thence into the foramen lacerum meclius situated in the angle 

 at the junction of the periotic, basioccipital, and basisphenoid. 

 That this was the point of entrance of the entocarotid artery 

 is clear from its close resemblance to the corresponding parts 

 in the skull of all of the Carnassiclentia. In this important 

 particular, it is therefore fundamentally different from the 

 Insectivora and Marsupialia, and like the Carnassidentia. The 

 foramen ovale is large and is placed as usual opposite to the 

 glenoid cavity, at a considerable distance from the posterior 

 edge of the alisphenoicl. Just in advance of this foramen, and 

 almost within the same aperture, is a small, but distinct, fora- 

 men leading into the antrum of the basisphenoid. In the 

 opossum, this foramen is large and opens further in advance 

 of the foramen ovale, but is connected with it by a distinct 

 groove. Its office in this latter species is the transmission of a 

 vein, a branch of which gains access to the cranial cavity 

 through a small foramen in the floor of the pituitary fossa, 

 There is no alisphenoid canal, but a slight groove marks the 

 forward course of the ectocarotid at this point. The foramen 

 rotundum and the sphenoidal fissure present separate openings, 

 and are situated in a deep groove above the pterygoids. The 

 opening of the rather large optic foramen is above, and con- 

 siderably in advance of these two. Above and in advance of 

 this, again, is the opening of the ethmoidal foramen for the 

 passage of a branch of the nasal nerve. 



The region of the glenoid cavity is considerably broken, 

 but there is enough preserved to indicate that there was a 

 strong postglenoid process, behind which is a small postglenoid 



