298 ZOOLOGY SECT. 



The columella is a small rod partly composed of cartilage and 

 partly of bone, the outer end of which is fixed into the inner 

 surface of the tympanic membrane, while the inner is attached to 

 a small aperture, thefenestra ovalis, in the outer wall of the auditory 

 capsule between the pro-otic and the opisthotic. 



Certain depressions or fossae and apertures or foramina are to be 

 observed in the skull. The foramen magnum, the parietal foramen, 

 and the orbits have been already mentioned. The posterior 

 temporal fossa is situated on either side of and above the foramen 

 magnum, bounded above and externally by the roofing bones, and 

 on the inner side by the bones of the occipital region. The inferior 

 temporal fossa is bounded internally by the pterygoid, and is 

 separated from the palatine foramen by the transverse. The 

 lateral temporal fossa is the wide space in the side wall of the 

 skull behind the orbit ; the bony bar which limits it above is 

 the superior temporal arch ; a bony inferior temporal arch is here 

 absent. The tympano-eustachian fossa, situated in the auditory 

 region, is bounded by the bones of that region together with the 

 quadrate. The posterior or internal nares 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 pre-maxilla3. 



Each ramus of the mandible consists of six bony elements in 

 addition to the slender persistent Meckel'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. ang) overlies the dorsal edge and upper half of the 

 outer surface of the articular. 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 membrane bones. 



The Jiyoid arch (vide Fig. 913 ; I. liy) 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. 908) the coracoids are flat bones 

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



