Lectures on the comparative anatomy and physiology of the vertebrate animals : delivered at the Royal College of Surgeons of England, in 1844 and 1846. Part 1 Fishes / by Richard Owen.

  • Owen, Richard, 1804-1892.
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on the comparative anatomy and physiology of the vertebrate animals : delivered at the Royal College of Surgeons of England, in 1844 and 1846. Part 1 Fishes / by Richard Owen. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    INTRODUCTORY LECTURE. damental group of Vertebrated animals, are never destined to quit the watery medium; these constitute the class of Fishes. A few species retain the primitive vermiform type, and have no distinct locomotive members; and these members, in the rest of the Piscine class, are small and simple, rarely adapted for any other function than the pro- pulsion or guidance of the body through the water. The form of the body is, for the most part, such as mechanical principles teach to be best adapted for moving with least resistance through a liquid medium. The surface of the body is either smooth and lubricous, or is covered by closely imbricated scales, rarely defended by bony plates or roughened by hard tubercles ; still more rarely armed with sjiiues. The central axis of the nervous system presents but one partial enlargement, and that of comparatively small size, at its anterior ex- tremity, forming the brain, which consists of a succession of simple ganglionic masses 46.), most of them exclusively appropriated to the function of a nerve of special sense. The power of touch can be but feebly developed in fishes. The organ of taste is a very in- conspicuous one, the chief function of the framework supporting it, or the hyoidean apparatus, relating to the mechanism of swallowing and breathing. Of the organ of hearing there is no outward sign ; but the essential part, tlie acoustic labyrinth, is present, and the semicircular canals largely developed within. The labyrinth is without cochlea, and is rarely provided with a special chamber, but is lodged, in common with the brain, in the cranial cavity. The eyes are usually large, but ai’e seldom defended by eyelids, and never served by a lachrymal organ. The alimentary canal is commonly short and simple, with its divisions not always clearly marked, the short and wide gullet being hardly distinguishable from the stomach. The pancreas, for the most part, retains its primitive condition of separate CEecal appendages to the duodenum. The heart consists essentially of one auricle and one ventricle, receiving the venous blood, and propelling it to the gills ; whence the circulation is continued over the entire body in vessels only, which are aided by the contraction of the surrounding muscular fibres. Tlie blood of fishes is cold ; its temperature being rarely elevated above that of the surrounding medium. Tlie coloured discs are sometimes subcircular {fg. 4. g\ sometimes subelliptical (A) or ellip- tic : comparatively largo, but not the largest amongst vertebrate animals. The primordial elongated renal glands are persistent, and secrete the urine from venous blood.