crus 

 endolymphatic sac 

 chorioid plexus 



medulla, 

 perilymphatic sac 



condyle 



notochord 



esophagus 



branchial columella 

 ligament 



anterior vertical semicircular canal 

 utriculus 



posterior canal ampulla 



sacculus 



basilar papilla 



perilymphatic cistern 



operculum 

 quadrate 



radix aorta 



ductus arteriosus 

 pulmonary artery 



pulmonary vein 



branchial membran 



superior sinus 

 utriculus 



perilymphatic canal 

 amphibian papilla 



horizontal semicircular 

 canal 



B 



basilar papilla' 



geno 



endolymphatic sac 

 chorioicJ plexus 



medulla 



'. r','' ■■ X (root and ganglion) 



perilymphatic sac 



Figure 13-20. Semidiagrammatic cross section of the otic region of the Bullfrog, Rano cotesbiano, 

 A, and the Clawed Toad, Xenopus laevis, B. (A after Witschi, 1956; B after Paterson, 1949) 



There is a large amount of calcified material in this endo- 

 lymphatic system. 



In the amphibian there is much modification in the audi- 

 tory system. In the Bullfrog larva the lungs are used to re- 

 ceive vibrations which are transferred through the bronchial 

 columella to the inner ear; in the adult the tympanic mem- 

 brane and columella are utilized. In various amphibians 

 different devices appear; some use the lower jaw, which 

 rests against the ground to transmit vibrations to the inner 

 ear; others use the forelimb, which is attached by means of 

 an opercular muscle or ligament to the ear capsule. Among 

 salamanders a tympanic membrane is lacking, but this is bet- 

 ter explained as loss than as a retention of the primitive state. 



Fossil forms dating back to the earliest known reptiles 

 and amphibians have a tympanic notch for a tympanic 

 membrane. The spiracle of the fish is high on the side of the 

 head in somewhat the same position as the otic notch of 

 fossil forms. In amniotes, the drum lies more posteriorly and 

 ventrally; because of this, there is a question whether it is 

 the same membrane in both positions. Primitively the drum 

 was nearly flush with the surface of the head, while in am- 

 niotes, with the exception of the turtles, it is sunk into the 

 head at the inner end of an external auditory meatus. 



It can be assumed that there has been a continuum in 

 fijnction from the original large "columella" (stapes), as- 

 sociated with the otic notch in the primitive amphibian, to 



SENSORY ORGANS 



407 



