MAY, 1921. AMERICAN MARSUPIAL, CENOLESTES OSGOOD. 101 



The foramina leaving the braincase include the sphenoidal fissure 

 and foramen rotundum, which already have been mentioned, the fora- 

 men ovale, transverse canal, entocarotid foramen, and ethmoid foramen, 

 in all of which the relations are generally similar to those in other mar- 

 supials although there is much variation, especially in diprotodonts. 



Ethmoid and turbinals. The cribriform plate of the ethmoid, as 

 previously stated, is more nearly upright than in the didelphids and 

 resembles that of Perameles. Its exact relations with the orbitosphenoid 

 and presphenoid are not distinguishable in the adult, but the bony floor 

 of the olfactory fossa is high and has a more rounded surface than in 

 other marsupials. It extends exactly parallel to the palate and hence 

 nearly at right angles to the anterior wall of the braincase. The prin- 

 cipal ethmo-turbinals visible in a simple section (PI. XVII, et.) are four 

 in number. The lowermost is relatively larger than in any other form 

 examined and is most nearly approached in Perameles nasuta. The 

 uppermost and longest of the ethmo-turbinals is relatively short, 

 extending forward only to the plane of the front of the last premolar. 

 This seems to be a resemblance to diprotodonts since it agrees with the 

 condition in Trichosurus and Petaurus. In the didelphids and in Phas- 

 cologale this upper ethmo-turbinal is very long, reaching as far forward 

 as the canines and almost completely inclosing the fenestrated part of 

 the maxillo-turbinals. In Perameles and Myrmecobius an intermediate 

 condition appears. 



The naso-turbinal offers no especial peculiarities. The maxillo- 

 turbinal springs from the nasal wall at a somewhat higher level than in 

 polyprotodonts and the nasal floor is narrower. 1 In these respects, 

 there is some variation among polyprotodonts but in general the 

 resemblance seems to be to diprotodonts. The maxillo-turbinal, as in 

 diprotodonts, is not largely enclosed by the anterior extension of the 

 ethmo-turbinal. The mesethmoid is a thin vertical plate of the usual 

 character. 



Nasals. These are long and slender, coming nearly to a point 

 anteriorly and being abruptly expanded posteriorly. Their anterior 

 extremities exceed the dorsal edges of the premaxillae and overhang the 

 anterior nares, reaching nearly as far forward as the lower anterior 

 extension of the premaxillae. In this they differ markedly from the 

 Dasyuridae, Thylacynidae, and Myrmecobiidae but are approached by 

 most diprotodonts, by the didelphids and especially by the peramelids. 

 The posterior expansions of the nasals include a slender curved prong 

 on each side projecting across the extraordinary vacuity which lies 



1 This is contrary to the observation of Broom (191 1, p. 318), whose material may 

 have been imperfect. 



