CROCODILIA. 19 



these pedicles are suspended vertically from the point of union of the mastoid and 

 paroccipital. 



The chief foramen in the occipital region is that called 'foramen magnum' (between 

 2 and 2, in fig. 2, T. VI), through which the nervous axis is continued from the skull. 

 On each side of the foramen magnum is a small hole, called i precondyloid foramen,' for 

 the exit of the hypoglossal nerve. External to this is a larger foramen, marked n in 

 fig. 2, for the transmission of the nervus vagus and a vein. Below this is the 

 6 carotid foramen' c. All these are perforated in the exoccipital. Below the condyle 

 there is usually a foramen, and sometimes two, for the transmission of blood-vessels. 

 Lower down, at the suture between the basioccipital and basisphenoid, is a larger and 

 more constant median foramen, indicated by the dotted line from e t ; it is the bony 

 outlet of a median system of eustachian tubes, peculiar to the Crocodilia. On each 

 side of the median eustachian foramen, and in the same suture, is a smaller foramen, 

 which is the bony orifice of the ordinary lateral eustachian tube. The membranous 

 continuations of the lateral eustachian tubes unite with the shorter continuation from 

 the median tube, and all three terminate by a common valvular aperture, upon the 

 middle line of the faucial palate, behind the posterior or palatal nostril. The large, 

 bony aperture of this nostril is formed by the pterygoids (24 in fig. 2). The carotid 

 canal, c, opens by a short bony tube into the tympanic cavity, and is described as the 

 ' eustachian canal' in the ' Lecons d'Anatomie comparee' of Cuvier. The artery 

 crosses the tympanic cavity, and enters a bony canal at its fore part, which conducts 

 to the ' sella turcica' in the interior of the cranium. 



The median eustachian foramen is described by Cuvier as the ' arterial foramen,'* 

 the canal from which divides and terminates in the c sella turcica.'f By MM. Bronn, 

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

 aperture of the posterior nostrils, j 



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 



* Ossemens Fossiles, torn, v, pt. ii, p. 133. 



t lb. p. 78. 



X Abhandlungen iiber die Gavialartigen Reptilien der Lias-formation, folio, 1841, pp. 12, 16, 44. 



