File:Image from page 136 of "On the anatomy of vertebrates (electronic resource)" (1866) (14732500566).jpg

Identifier: b20416039_001 Title: On the anatomy of vertebrates [electronic resource] Year: 1866 (1860s) Authors: Owen, Richard, 1804-1892 Subjects: Anatomy, Comparative Vertebrates Fishes Reptiles Mammals Birds Publisher: London : Longmans, Green Contributing Library: Wellcome Library Digitizing Sponsor: Wellcome Library

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Text Appearing Before Image: ons of these elements, the more expanded mes- and pros-encephalahaving their bony ring or arch completed by a centrum below anda spine above. One neurapophysis (alisphenoid) transmits thetrigeminal nerve, the other (orbitosphenoid) the optic nerve: thefourth or anterior neural arch ( os en ceinture and ethmoideof Cuvier) encompasses the foremost segment of the brainas the exoccipitals do the hindmost; and they give passageto the olfactory nerves. Ossification of this ring of bone beginsin its lateral halves: the essential relations and functions being;those which characterise the bones which in bony fishes will bedescribed as c prefrontals. Beneath, and supporting them, is apair of bones which may be regarded as a mesially divideds centrum (vomer): and above is a pair of bones which may be 1 exxxix. Ce crane ne saccorde pas plus avec la theorie des trois, des quatre, oudes sept vertebres, meme avec cello duno vertebre, quavec cellc do lidentitc donombre des os, vol. v. pt. ii. p. 391.

Text Appearing After Image: 92 ANATOMY OF VERTEBRATES. regarded as a mesially divided neural spine (nasal). Thus may bediscerned four cranial segments having the essential characters andrelations of the neural arch of the type vertebra. The upper, 22,and lower, 30, jaws, the hyoid, 40, and scapulocoracoid, 50-52, fig. 42,constitute four inverted arches; but their vertebral relations willbe better understood in the composition of the skull in bony fishes. § 30. Skull of Osseous Fishes.— The head is larger in proportionto the trunk in fishes than in other vertebrate classes ; it is usuallyin form of a cone, figs. 34, 38, whose base is vertical, directed back-ward, and joined at once to the trunk, and whose sides are three innumber, one superior, and two lateral and inferior. The cone isshorter or longer, more or less compressed or squeezed from sideto side, more or less depressed or flattened from above downward,with a sharper or blunter apex, in different species. The base ofthe skull is perforated by the hole

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