. Chordate morphology. Morphology (Animals); Chordata. 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','' â â 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
. Chordate morphology. Morphology (Animals); Chordata. 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','' â â 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 larg
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