500 MANUAL OF ZOOLOGY sect. 



the palatine in front and the ali-sphenoid behind. The 

 lachrymals are small bones, one situated in the anterior 

 wall of each orbit, perforated by a small aperture — the 

 la ch rym al 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 

 vertical or ascending portion, which bears the articular 

 surface or condyle for articulation with the glenoid cavity 

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

 coronoid process. The angle where the horizontal and as- 

 cending processes meet gives off an inward projection or 

 angular process. 



The Avoid, 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. 300) are fewer 

 than in the pigeon. There is a broad thin triangular scapu- 

 lar, the base or vertebral edge of which has a thin strip of 

 cartilage (the supra-scapular cartilage) continuous with it. 

 Along the outer surface runs a ridge, the spine ; the spine 

 ends below in a long process, the acromion process (a), 

 from which a branch process or metacromion {ma) is given 



