No. 472] ANATOMY OF CRYPTOBRANCHUS 295 



forms an arc that is almost exactly concentric with the arc of the 

 premaxilltie and maxillae, except that there is a shulit deprosion 

 in the middle where the two vomers meet. Tlic anterior half of 

 the median edge of each vomer is elevated dorsally into a ridj^e, 

 and the median elevation formed bv the imion of these ridges sep- 

 arates the nasal chamber into its two parts, and unites the vomers 

 below with the nasals and the premaxilhp above. It forms, in 

 other words, the bony nasal septum. 



The prooiics (Po.) are two small bones of irregular shape that 

 form the antero-dorsal borders of the auditory capsules. Even 

 in the adult they are largely composed of cartilage, so that in the 

 dried skull they scarcely show from either the dorsal or the ventral 

 side. They are more closely united to the parasphenoid than to 

 any other bone, but they also articulate with the cartilaginous pos- 

 terior end of the ethmoid, with the parietals, witli the s(|uainous 

 bones, and, possibly to a slight extent with the j)t("i vooi.l>. Tlirre 

 lire several canals that lead from the exterior to ilir cranial ( aviiy. 

 in the neighborhood of the prootic. Of tlicM- ilir lari:t'>t has 



and is said by Osawa to be the trigeminal foranuMi. it is a l.irak 

 in the median border of the prootic, i-atlicr than an actual canal 

 through the bone. The only other canal in thi. l.onr that can be 

 made out without dilficulfy is the facial, whi.-h lies in the edge of 

 the bony part of the i)n)()tic, just dorsal to the carotid canal, and 

 runs transversely through die l)one to the cranial ca\it_v. 



Columella auris is the name given to two very >m:dl bones that 

 are found in connection wiili die anditorv capsules. Each col- 

 umella is fan-shaped or ])almate in oulline, and. on account of its 

 minute size and loose attachment to the rest of the skull, is easily 

 lost in the preparation of the skull. The broad i)art of the hone 

 is connected by cartilage with the foramen ovale of the auditory 

 capsule, while the narrow end (the handle of tlu^ fan i proj.M t- lat- 

 erally and, accor.ling to Osawa. is comiected by cartihiL^e with the 

 quadrate, though this latter point couhl not be detennine.l in the 

 present .pecic.'. 'Vhr colunu-lla doe. not .how in either ..f the fig- 

 ures of the skull. 



The cartilaginous cranium will now be .le.crihe.l. It may be 



