46 THE FROG chap. 



head, the latter firmly fixed to the inner face of the tym- 

 panic membrane. The inner end of the handle is tipped 

 with cartilage, and is attached to a small cartilaginous nodule, 

 the stapes (si), which is inserted into an aperture in the 

 auditory capsule known as the fenestra ovalis {fen. ov). With 

 care the columella can easily be removed with small forceps, 

 in a wet skull, and examined under a magnifying glass. 



The shoulder-girdle has the form of an inverted arch 

 encircling the anterior region of the trunk, and having its 

 dorsal ends turned inwards so as partly to cover the second 

 to the fourth vertebrae (Figs. 8 and ii). The dorsal region, 



s.scp 



efi.cor 



Fig. II. — Diagrammatic transverse section through the shoulder -girdle. 

 coy, coracoid ; ep. cor. epicoracoid ; gL glenoid cavity ; hu. humerus ; scp. scapula ; 

 J. scp. supra-scapula ; v. 3^ third vertebra. 



on each side, is formed by a broad plate, the supra-scapula 

 is. scp), or upper blade-bone. It is mostly formed of bone, 

 but its free edge consists of cartilage which, when dried, is 

 seen to be impregnated with a granular deposit of lime-salts. 

 This rough, brittle tissue is called calcified cartilage, and is 

 distinguishable from true bone, which has usually a smooth, 

 enamelled surface. 



Connected with the ventral end of the supra-scapula and 

 passing vertically downwards is a flat bone, broadened at 

 each end, the scapula or blade-bone (Fig. it, scp: Fig. 1 2, S). 



