SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 



337 



10. Optic foramen confluent with 

 sphenoidal fissure. 



11. Basisphenoid and alisphenoid 

 ridged as in existing marsupial 

 carnivores and unlike the struc- 

 ture of this region in the pla- 

 centals. 



1 2. Posterior border of palate thick- 

 ened. 



10. Not exclusively marsupial, al- 

 though characteristic of that 

 order. 



11. "In the marsupial Carnivora 

 the basisphenoid is relatively 

 longer than in the placental 

 Carnwora, and, at its posterior 

 part, it sends a ridge down- 

 ward from that part of each 

 lateral margin which is not 

 overlapped or covered by the 

 base of the alisphenoid, the 

 suture of which long continues 

 distinct. These ridges, with 

 the alisphenoid, render the 

 whole under surface of the 

 basisphenoid canaliculate, or 

 concave transversely ; the basi- 

 sphenoid is flat beneath in the 

 placental Carnivore*, and that 

 part of the base of the skull is 

 made canaliculate by the de- 

 velopment of the ectopterygoid 

 plate from the alisphenoid ; 

 these plates exist likewise in 

 the marsupials, but, as they 

 extend backwards to join the 

 alisphenoid bullse, they diverge 

 from the basisphenoid ridges 

 and are external to them." 

 (Owen, Phil. Trans. Royal 

 Soc. London, Vol. 149, p. 315, 

 1860.) 



1 2. Characteristic of the majority oi 

 existing marsupials. Present 

 also in some of the Creodonta 

 (Mesonychidae). 



