. The biology of the amphibia. Amphibians. 336 THE BIOLOGY OF THE AMPHIBIA sacculus may be constricted into a smaller upper and a larger lower vesicle. The utriculus gives rise to the semicircular canals which are arranged in the three planes characteristic of all gnathostomes (Fig. 122). The anterior and posterior canals are arranged vertically and at an angle of 90 degrees to one another and 45 degrees to the median plane of the animal's body. The third is at right angles to the other two and lies horizontally on their outer side. The sacculus develops a small evagination, the lagena, which
. The biology of the amphibia. Amphibians. 336 THE BIOLOGY OF THE AMPHIBIA sacculus may be constricted into a smaller upper and a larger lower vesicle. The utriculus gives rise to the semicircular canals which are arranged in the three planes characteristic of all gnathostomes (Fig. 122). The anterior and posterior canals are arranged vertically and at an angle of 90 degrees to one another and 45 degrees to the median plane of the animal's body. The third is at right angles to the other two and lies horizontally on their outer side. The sacculus develops a small evagination, the lagena, which is destined to form the cochlea of higher vertebrates. Fig. 122.—Membranous labyrinth of the inner ear of Megalobatrachus japoni- cus. The left labyrinth viewed from the outside. , ampulla anterior; , ampulla lateralis; , ampulla posterior; , canalis semicircu- laris anterior; , canalis semicircularis lateralis; , canalis semicircularis posterior; , ductus endolymphaticus; Lag., lagena; , nervus acusti- cus; , pars basilaris; , pars neglecta; , recessus utriculi; Sac, sacculus. (After Okajima.) The sense organs arise from a common anlage which divides into seven or eight areas. A patch of sense cells comes to lie at one end of each of the semicircular canals. Each is covered by a gelatinous cap, the cupula, and the canal at this point is swollen into an ampulla. The utriculus becomes equipped with a macula utriculi and a smaller m. neglecta (which is doubled in the caecili- ans), the sacculus retains a macula sacculi and a papilla lagenae. These four sense areas of the utriculus and the sacculus have the sense cells extended into long processes over which lie a gelatinous cover and in addition a layer of "hearing sand," crystals of calcium carbonate. Amphibia differ remarkably from fish in possessing an additional sense area, the papilla basilaris, which splits off from the papilla lagenae. It is covere
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
