Identifier: treatiseonzoolo09lank (find matches)
Title: A treatise on zoology
Year: 1900 (1900s)
Authors: Lankester, E. Ray (Edwin Ray), Sir, 1847-1929 Bather, Francis Arthur, 1863-1934 Goodrich, Edwin S. (Edwin Stephen), 1868-1946
Subjects: Zoology
Publisher: London : A. & C. Black
Contributing Library: Robarts - University of Toronto
Digitizing Sponsor: University of Toronto

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tive groups fulcral scales are found on the extreme anterior edge of some or all of the fins, especially on the dorsal edge of the caudal. The fulcra are quite peculiar to this Division, and consist of a double series of elon-gated scales (Fig. 286); often the opposing scales fuse to Y-shaiDed fulcra (Fig. 280). In the gular series of plates the mostanterior median is gener-ally large and the pairedseries become very numer-ous and narrowed (Figs. 285-7). They are con-verted into freely movablebranchiostegal rays. Thetwo foremost may belonger than the others,but never occupy thespace between the tworami as in the Osteo-lepidoti, Coelacanthini,and Polypterini, and areprobably not homologous^^■ith the paired gulars ofthe first two Orders. Thebody-scales and dermalplates of the more primi-tive forms are of the trueganoid structure (p. 218).Usually the scales havepeg and socket articula-tions, and the peg oftenappears as the continua-tion of an inner thickei ed ridge. caudal. Those cases
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scales, like the A C TINOP TEN YGII 305 branchiostegal rays and the fulcra, may in the course of divergentevohition undergo great nioditication and reduction. In the primi-tive forms the cranial bones conform to the ordinary Teleostomeplan ; the preoi)erculum does not cover the cheek, as is so often thecase in tlie Osteolepidoti. The brain in the Actinopterygii acquires a very characteristicstructure. The preponderance of the hind- and mid-brain over thefore-brain, which has already been noticed in the Teleostomes ingeneral, becomes more pronounced, especially in the Teleostei.There is a large cerebellum, which, instead of bulging almost entirel)on the surface, as, for instance, in the Selachian, extends forwardsand inwards into the ventricle of the mesencephalon. In the

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