xii PHYLUM CHORDATA 495 



squamosal and thus complete the zygomatic arch, is a 

 separate bone in the young, the malar or jugal (ju.). 



The rest of the narrow bony palate, forming the roof of the 

 mouth and the floor of the nasal cavities, is formed by the 

 palatine plates of the palatine bones (pal.). The ptery golds 

 (pt.) are small irregular bones, each of which articulates 

 with the palatine in front and the alisphenoid behind. 

 The lacrymals are small bones, one situated in the anterior 

 wall of each orbit, perforated by a small aperture the 

 lacrymal foramen. 



The mandible, or lower jaw, consists of two lateral halves 

 or rami, which articulate with one another in front by a 

 rough articular surface or symphysis, while behind they 

 diverge like the limbs of a letter V. In each ramus is a 

 horizontal portion (anterior) which bears the teeth, and a 

 verticalor ascending portion, which bears the articular sur- 

 face or condyle (con.) for articulation withthe glenoid cavity 

 of the squamosal ; in front of the condyle is the compressed 

 coronoid process. The angle where the horizontal and 

 ascending processes meet gives off an inward projection or 

 angular process (ang. pro.). 



The hyoid, which, as in the Pigeon, is the only other 

 post-oral visceral arch represented in the adult, consists of 

 a stout thick body or basi-hyal, a pair of small anterior 

 cornua or cerato-hyals, and a pair of long backwardly directed 

 cornua or thyro-hyals. 



The auditory ossicles, contained in the cavity of the middle 

 ear, and cut off from the exterior, in the unmacerated skull, 

 by the tympanic membrane, are extremely small bones, 

 which form a chain extending, like the columella auris of 

 the Pigeon, from the tympanic membrane externally to the 

 fenestra ovalis internally. 



The elements of the pectoral arch (Fig. 278) are fewer 



