314 



PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 



aiiditoria interna pierce the bone. On both sides the tympanic sinuses in the alisphe- 

 noid, 6, are exposed ; and their concordance with those in the Basyuri is very clearly 

 exemplified on the left side, in which the tympanic bone, 28, is preserved, showing its 

 characteristic shape and relative position behind and external to the alisphenoid 

 bulla, 6. 



The canal of the meatus [k) external to the tympanic, is excavated in the outwardly 

 produced base of the zygoma, behind the postglenoid process {I), for an extent resem- 

 bling that in the Dasyuri, but much greater than in the Dog or other placental 

 Carnivora. 



Another character distinctive of the marsupial order is the position of the entocarotid 

 canal [m), which perforates the outer and back part of the basisphenoid, s * : this orifice 

 is lodged in a fossa between the basioccipito-sphenoid and the bulla auditoria in Thyla- 

 cinus and Lasyurus {ib. fig. 2, m), and it presents exactly the same position, and per- 

 forates the same part of the basisphenoid, in Tliylacoleo. 



In the genus Felis the entocarotid enters the base of the skull at the fore-part of the 

 foramen jugular notching the part of the petro-tympanic bulla at the fore-part of that 

 foramen. In the Hysena, as in the Viverrines, the entocarotid notches or perforates 

 the tympanic bulla in advance of the jugular foramen close to the side of the basi- 

 occipital: it perforates the same part of the tympanic bulla in the Otter and other 

 Mustelines. 



The foramen ovale pierces the base of the alisphenoid immediately anterior to the 

 bulla in the marsupial Carnivora^ and is divided by a ridge from the carotid canal in 

 the Dasyuri; it presents the same relations in Thylacoleo (Plate XIV. fig. \,n), and the 

 base of the ridge (ib. s) also remains to show the existence of that character. 



The interval between the foramen ovale (Plate XI. fig. 1, 7i) and foramen rotundum 

 (ib. is relatively much greater in the marsupial than in the placental Carniwra. In 

 the genus Felis, they are separated from each other only by the base of the ridge or 

 rising of bone extending from the ectopterygoid towards the glenoid cavity, and the 

 foramen is on the same transverse line with the anterior boundary of that articulation ; 

 in the Hyaena, Viverrines, and Dog, it is a little in advance of the same boundary ; in the 

 Otter it opens externally into a fossa common to it with the foramen lacerum anterius 

 (or for. ophthalmicum). In the Thylacine and Dasyures the foramen rotundum is distinct 

 both within and without the cranial cavity from the foramen lacerum anterius, and is 

 far in advance of the glenoid cavity. It presents the same relative position in the 

 Thylacoleo (Plate XI. fig. 1,^). 



In Felis the foramen rotundum is larger than the foramen opticum ; in Dasyurus 

 it is much smaller ; and this is the case also with the Thylacoleo (Plate XI. fig. 1), 

 although the foramen opticum [q) is relatively smaller than in the Dasyurus ursinus. 



* " The carotid canals pierce the body of the sphenoid, as in Birds, and terminate in tlie skull very close 

 together behind the sella turcica.''^ — Zoological Transactions, vol. ii. (October, 1838), p. 390. See also 

 Mr. TuHNEii's can'ful and minute account of the "Foramina at the Base of the Skull" in Zoological Pro- 

 ceedings, May, 184'8, p. 64. 



