CROCODILTA. Ill 



Kaup, and De Blainville, the median Eustachian foramen is contended to be the bony 

 aperture of the posterior nostrils.* 



The results of the dissections and injections of recent Crocodiles and Alligators, by 

 which I have been able to rectify the discrepant opinions regarding the carotid, 

 eustachian, and naso-palatal foramina, and which have led to the discovery of a third 

 median eustachian canal, or rather system of canals, between the tympanic cavities and 

 fauces, peculiar to the Crocodilian Reptiles, are given In detail in the ' Philosophical 

 Transactions' for 1850. The complexity of the superadded system has doubtless 

 chiefly contributed to mislead the justly-esteemed authorities who have believed that 

 they saw in it characters of the carotid canals or of the posterior nasal passages. The 

 eustachian apparatus in the Crocodilia may be briefly described as follows : From the 

 floor of each tympanic cavity two air-passages are continued ; the canal from the fore part 

 of the cavity extends downwards, backwards, and inwards, in the basisphenoid, which 

 unites with its fellow from the opposite tympanum, to form a short median canal, which 

 descends backwards to the suture between the basisphenoid and the basioccipital, where 

 it joins the median canal formed by the union of the two air-passages from the back 

 part of the floor of the tympanum, which traverse the basioccipital. The common canal 

 formed by the junction of the two median canals descends along the suture to the 

 median foramen e t, fig. 2, PI. 1 A. The air-passage from the back part of the tym- 

 panum, which traverses the basioccipital, swells out into a rhomboidal sinus in its 

 convergent course towards its fellow, and from this sinus is continued the normal 

 lateral eustachian canal, which, on each side, terminates below in the small aperture, 

 external to the median eustachian foramen. 



That part of the outer surface of the skull which is covered by the common 

 integument is more or less sculptured with wrinkles and pits in the Crocodilia .• the 

 modifications of this pattern are shown in PI. A 2, fig. 1, in the nilotic Crocodile, and 

 in PI. 1 A, in the eocene Crocodile from Hordwell. The flat platform of the upper 

 surface of the cranium is perforated by two large apertures, surrounded by the bones 

 numbered 7, 8, 11, 12; these apertures are the upper outlets of the temporal fossae, 

 divided from the lower and lateral outlets by the conjoined prolongations of the 

 mastoid 8 and postfrontal 12: if ossification were continued thence to the parietal 7, 

 the temporal fossae would be roofed over by bone, as in the Chelones. In old 

 Crocodiles and Alligators there is an approximation to this structure, and the upper 

 temporal apertures are much diminished in size. In the Gavials (PI. 1, fig. 1 a) they 

 remain more widely open, and, in the fossil Gavials of the secondary strata, they are 

 still wider, as seen in fig. 2 « ; by which the structure of the cranium approaches more 

 nearly to that of the Lacertian reptiles, where the temporal fossa is either not divided 

 into an upper and lateral outlet, or is bridged over by a very slender longitudinal bar 

 from the postfrontal to the mastoid. The lateral outlets of the temporal fossae (PI. 1 J, 



* Abhandlungen iiber die Gavialiirtigen Reptilien der Lias-formation, folio, 1841, pp. 12, 16, 41. 



