THE SKELETON OF THE FROG. THE HYOID. 161 



of which there are developed two membrane bones and one 

 cartilage, bone. The cartilage bone is the mento-meckelian 

 (fig. 26, A, 14), a very small ossification at the extreme anterior 

 end. The membrane bones are the angulo-splenial and the 

 dentary. The angulo-splenial is a strong flat bone which forms 

 the inner and lower part of the mandible for the greater 

 part of its length. Its dorsal surface is produced into a slight 

 coronoid process. The dentary (fig. 26, A, 15) is a flat 

 plate which covers the outer surface of the anterior half of the 

 mandible, as far forwards as the mento-meckelian. The lower 

 jaw is devoid of teeth. The part of Meckel's cartilage which 

 in most vertebrates ossifies, forming the articular bone, remains 

 unossified in the Frog. 



THE HYOID APPARATUS. 



The hyoid of the adult Frog is formed of the modified 

 hyoid and branchial arches of the tadpole. It consists of a 

 broad thin plate of cartilage, the basilingual plate (fig. 29, 

 B, 1), drawn out into two pairs of long processes, the comua. 

 The basilingual plate is broader in front than behind, and is 

 formed from the fused ventral ends of the hyoid and branchial 

 arches of the tadpole. 



The anterior cornua (fig. 29, B, 2) form a pair of long 

 slender cartilaginous rods which project from the body of the 

 hyoid at first forwards, then backwards, and finally upwards 

 and somewhat forwards again, to be united to the auditory 

 capsules just below the fenestrae ovales. They are formed 

 from the dorsal portion of the hyoid arch of the tadpole and 

 are homologous with the cerato-hyals of the Dogfish. 



The posterior cornua form a pair of straight bony rods 

 diverging outwards from the posterior end of the basilingual 

 plate. They are formed from the fourth branchial arches of 

 the tadpole, and differ from the rest of the hyoid apparatus 

 in being well ossified. 



R. 11 



