46 THE FROG CHAP. 



membrane is a small, hammer-shaped rod, the columella 

 (Figs. 9 and 10, col), having a bony handle and a cartila- 

 ginous head, the latter firmly fixed to the inner face of 

 the tympanic membrane. The inner end of the handle 

 is tipped with cartilage, and is attached to a small 

 cartilaginous nodule, the stapes (st), which is inserted 

 into an aperture in the auditory capsule known as the 

 fenestra ovalis (fen. ov). With care the columella, in a 

 wet skull, may easily be removed with small forceps, and 

 examined under a magnifying glass. 

 The shoulder-girdle has the form of an inverted 



FIG. ii. Diagrammatic transverse section through the shoulder-girdle of a 



Frog, (x 2.) 



cor. coracoid ; ep. cor. epicoracoid ; gl. glenoid cavity ; hu. humerus ; scp. scapula ; 

 s. scp. supra-scapula ; v. j, third vertebra. 



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 n). 

 The dorsal region, on either side, is formed by a broad 

 plate, the supra-scapula (s. 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 distin- 

 guishable from true bone, which has usually a smooth, 

 enamelled surface. 



