320 ZOOLOGY SECT. 



interned nnres are bounded posteriorly by the palatines. The 

 anterior or external nasal aperture is situated at the anterior 

 extremity of the skull bounded by the nasals and premaxillae. 



Each ramus of the mandible consists of six bony elements in 

 addition to the slender persistent MecJcel's cartilage. The proximal 

 element is the articular (art) which bears the articular surface for 

 the quadrate, and is produced backwards into the angular process. 

 The angular (ang) is a splint-like bone covering the ventral edge 

 and the lower half of the outer surface of the articular. The supra- 

 angular (s. any) overlies the dorsal edge and upper half of the 

 outer surface of the same bone. The dentary (dent) forms the main 

 part of the distal portion of the mandible, and bears all the mandi- 

 bular teeth. The splenial is a flat splint applied to the inner face 

 of the dentary. The coronary (cor), a small, somewhat conical 

 bone, forms the upwardly directed coronoid process immedi- 

 ately behind the last tooth. All these, with the exception of the 

 articular, are investing bones. 



The hyoid apparatus (vide Fig, 968; b. hy) consists (1) of a median 

 cartilaginous rod, the ~basi-hyal, (2) of the anterior cornua, elongated 

 cartilaginous rods which, connected ventrally with the basi-hyal, 

 curve round the gullet and end in close relation with the ventral 

 surface of the auditory capsule, (3) of the middle cornua, rods of 

 cartilage ossified at their proximal ends, and (4) of the posterior 

 cornua, cartilaginous rods arising from the posterior edge of the 

 basi-hyal and passing backwards and outwards. The middle cornua 

 are vestiges of the first, the posterior of the second, branchial arch. 



In the pectoral arch (Fig. 963), the coracoids are flat bones 

 articulating with the antero -lateral border of the sternum, and 

 bearing the ventral half of the glenoid cavity (glen) for the head of 

 the humerus ; a cartilaginous epicoracoid (ep. cor) element lies on 

 the inner side of the procoracoid and coracoid ; a large gap 

 or fenestra divides each into a narrow anterior portion the 

 procoracoid (pr. cor), and a broader posterior portion, the coracoid 

 proper (cor). The scapulcv (sc) articulate with the outer ends of 

 the coracoids, and each bears the dorsal half of the glenoid cavity. 

 Dorsally the scapulae become expanded, and each has connected 

 with it a thin plate of partly calcified cartilage the suprascapula 

 (supra, sc), which extends inwards towards the spinal column on 

 the dorsal aspect of the body. An element not hitherto met with, 

 except in the Stegocephala (p. 302), is the interclavicle or episternum 

 (epist), a cross-shaped investing bone, the stem of which is longi- 

 tudinal and is in the posterior portion of its extent closely applied 

 to the ventral surface of the anterior part of the sternum, while the 

 cross-piece is situated a little in front of the scapula. The clavicles 

 (cl) are flat curved bones articulating with one another in the middle 

 line and also with the anterior end of the interclavicle. The bones 

 of the fore-limb consist of a proximal bone or humerus, a middle 



