. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry 8o3 In frogs and toads but not in urodcles, the spiracular cleft enlarges into the tympanic cavity, which is not properly a ''middle ear" since no external ear is present. A large external ear drum, connected by a columella with the internal ear, is placed at the level of the skin, and is consequently much exposed to injury. The first true auditory nerve terminals appear in amphib- ians in the form of the macula neglecta and the papilla
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Ports of Entry 8o3 In frogs and toads but not in urodcles, the spiracular cleft enlarges into the tympanic cavity, which is not properly a ''middle ear" since no external ear is present. A large external ear drum, connected by a columella with the internal ear, is placed at the level of the skin, and is consequently much exposed to injury. The first true auditory nerve terminals appear in amphib- ians in the form of the macula neglecta and the papilla basilaris, the latter structure being of importance since it is the forerunner of the organ of Corti which becomes incorporated within the lagena that later coils to form the cochlea Fig. 703. Lateral-view diagrams of the left labyrinth of the ear. a, tele- ost; b, frog; c, turtle; d, crocodile; e, bird; F, mammal. 1, macula utriculi; 2, macula sacculi; 3, macula lagenae; 4, basal papilla. (After Hesse.) The macula neglecta continues to be represented in reptiles and birds but disappears in mammals. The ear drum becomes sunken in reptiles and birds, forming a pit which is the beginning of the external auditory canal. Some lizards and crocodiles have an earfold at the margin of the pit which foreshadows the pinna of the mammalian ear. By means of this fold an alligator is enabled to close the short auditory canal while submerged in water. "Horned owls" and certain other birds have the earfold supplemented by upstanding feathers. The tympanic cavity of snakes and legless lizards is much reduced or absent, since direct contact with the ground is the means employed for the reception of seismic vibrations on the part of these highly thigmotactic animals. In birds and crocodiles the two Eustachian canals form a median duct that enters the mid-dorsal region of the pharynx by a. Please note that these images are extracted from scanned page images that may have been di
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
