1<)]().] Cranial Foramina in Marsupials. 223 



III, IV, \l and the frontal V)ran('li of the trigeminus (\\). The opposite 

 anterior lacerate foramina are confluent so that a bristle may be passed 

 through the skull at this point. 



The foramen roiundum (for the maxillary branch of the trigeminus, V2) 

 is generally a very prominent tubular oj^ening directed forward at some little 

 distance behind the foramen lacerum anterius. In the interior of the skull 

 it is continuous with a longitudinal groove or fossa for the Gasserian ganglion 

 (V1-3), on either side of the sella turcica and external to the carotid foramen. 



Transverse canal. — There is frequently a prominent foramen or canal 

 whic-h tunnels the floor of the basisphenoid transversely, and may be desig- 

 nated as the "" transverse canal.''' In the opossum, according to Wortman, 

 (1902, p. 440) its office 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." This canal strongly suggests the "canalis transversus" 

 of Simplicidentate rodents, which likewise, according to Tullberg, transmits 

 a vein (Weber, 1904, p. 474). To judge from Sinclair's description (1901) 

 of the skull of Borhijania, the transverse canal appears to be absent in some 

 at least of the fossil carnivorous Marsupials of Patagonia, but it is present in 

 the Diprotodonts examined as well as in Didelphis. 



No true alisphenoid canal perforates the alisphenoid bone, but in the 

 opossum a slight groove just in front of the transverse canal may mark the 

 forward course of the ectocaroted, or maxillary branch of the carotid artery. 



Posterior to the transverse canal and occupying approximately the posi- 

 tion of the foramen ovale in the dog lies the entocarotid canal which per- 

 forates the basisphenoid, entering forwards. This has long been knoAvn as 

 a constant feature of the Marsupial skull; but Wincza (1898, quoted by van 

 Kampen, 1905, p. 383) reports that in Acrobates pygmmis the carotid 

 enters the skull in the same maimer as in most Placentals, i. e., through the 

 foramen lacerum medium. 



Lying between the petrosal and the basioccipital is a foramen which may 

 provisionally be termed the posfcrior carotid foramen, which probably trans- 

 mits a posterior branch of the entocarotid. It is present in all the Polyproto- 

 donts examined, but was not recognized in the Diprotodonts. 



Perforating the posterior part of the alisphenoid near the alisphenoid 

 bulla and looking either forward or outward and downward toward the inner 

 side of the mandible is the foramen ovale, for the mandibular branch of the 

 trigeminus (V3). 



The Eustachian canal lies between the tympanic expansion of the ali- 

 sphenoid and the petrosal. It is frequently lodged in a groove on the internal 

 side of the tympanic portion of the alisphenoid, issuing from the tympanic 

 cavity, and running forward and inward. 



