376 



CROCODILIA. 



The eustachian passages * are surrounded by bone and open close to- 

 gether into the pharynx by a median opening behind the posterior nares. 

 From this opening (Fig. 206) there passes off three tubes, one median and 

 two lateral. The median tube (o) is contained in a canal between the 

 basioccipital and basisphenoid, where it bifurcates into an anterior branch 

 (q) which passes into the basisphenoid, and a posterior into the basi- 

 occipital (r). The anterior branch divides into a right and left canal which 

 open into the tympanic cavity. The posterior also bifurcates and each of 



the canals so formed (s) rims to open 

 into the tympanic cavity by a tube 

 (<), wliich joins one of the two lateral 

 canals (p) which pass from the pha- 

 ryngeal opening. 



The columella is bony and 

 extends from the fenestra ovalis 

 to articulate with a trifid car- 

 tilage — the extra-columellar car- 

 tilage (infra- + extra- + supra- 

 stapedial), which is attached to 

 the tympanic membrane. 



The lower process of this cartilage is 

 continuous with a partly cartilaginous, 

 partly fibrous cord which Ues in a 

 groove or canal on the hinder surface 

 of the quadrate immediately behind 

 the siphonimn, and is connected with 

 the OS articulare of the lower jaw. 

 The upper cartilaginous part of this 

 cord is called by Huxley the styloid 

 cartilage. In the embryo this cord 

 was a continuous cartilaginous con- 

 nection between the lower process 

 (infra-stapedial) of the extra- colvunel- 

 lar cartilage and Meckel's cartilage. 



Fig 205. — Ventral view of skull of an alliga- 

 tor {Caiman laiirostris) to show eusuclial 

 choanae (after Reynolds). 1 premaxUla ; 

 3 maxilla ; 3 palatine ; 4 pterygoid ; 5 

 choanae ; 6 transpalatine ; 7 posterior, 

 8 anterior palatine vacuity ; 9 basioc- 

 cipital ; 10 median opening of the eusta- 

 chian tube ;/i jugal; IS quadrato-jugal ; 13 

 quadrate ; 20 lateral temporal fossa ; SI 

 vascular channels leading into openings 

 of alveolar sinus. 



The hyoid consists of a cartila- 

 ginous body and a pair of partly 

 ossified cornua. 

 The lower jaw consists of six bones, the dentary which suturally 

 unites with its fellow at the symphysis and bears the sockets in 

 which the teeth are implanted ; the splenial {operculare), the 

 angular, the surangular, the articular which is pneumatic, and 

 the coronoid. In the long-snouted forms the splenial may take 

 part in the symphysis. 



Owen, PUL Trans., 1850; v. Beneden, ^rc^i. de £jo%te, 3, 1882, p.497. 



