xra 



PHYLUM CHORDATA 



263 



the frame of a tambourine supports the parchment. Inserted into 

 the fenestra ovalis is a nodule of cartilage, the stapes (stp.), to 

 which is attached the inner end of a small hammer-shaped structure, 

 the columella (COL), the 

 handle of which is ossi- 

 fied, while its carti- 

 laginous head, or extra- 

 columella, is fixed to the 

 inner surface of the tym- 

 panic membrane. 



The comparison of the 

 Frog's skull with those 

 of Fishes is facilitated 

 by a study of its de- 

 velopment. In the tad- 

 pole or larval Frog there 

 is a cartilaginous cranium 

 (Fig. 935) connected on 

 each side with a stout 

 inverted arch, like the subocular arch of the Lamprey or the 

 palatoquadrate of Chimsera or Ceratodus, and, like them, de- 

 veloped from the dorsal region of the mandibular arch. The 



br, 



FIG. 935. Skull of Tadpole, au. cp. auditory capsule 

 br. 1 4, branchial arches ; c. hy. ceratohyal ; col. 

 columella ; mck. Meckel's cartilage ; olf. cp. olfactory 

 capsule ; opt . for. optic foramen ; or. pr. orbital pro- 

 cess of suspensorium ; ot. pr. otic process ; pal. pig. 

 palato-pterygoid bar ; qu. quadrate ; stp. stapes. 

 (After Marshall, slightly altered.) 



JGi 



FIG. 936. Rana esculenta. The shoulder-girdle from the ventral aspect. Cartilage dotted. 

 Co. coracoid ; Co 1 , epicoracoid ; Cl. clavicle ; Ep, omosternum ; Q. glenoid cavity ; Fe 

 fenestra between clavicle and coracoid ; KC. cartilage separating scapula and clavicle ; 

 Kn. xiphisternum ; m. junction of epicoracoids ; S. scapula ; St. sternum. (From Wieders- 

 heim's Comparative Anatomy.) 



quadrate region (qu) of this primary upper jaw is well in front 

 of the eye, the axis of the suspensorium being inclined for- 



R 2 



