. Animal physiology. Physiology, Comparative; Physiology, Comparative. GENERAL STRUCTURE OF FISHES. 83 nishing the resistance which it offers to their progress, and of increasing the extent of the oar-like surface, by the stroke of which the body is propelled forwards (Chap. xn). 99. The preceding figure of the skeleton of the Perch shows the bony apparatus, by which this extended surface is supported. The spinous processes of the vertebrae, which pro- ject upwards from the vertebral column, are long, and are con- nected with another set of bones, which continue them, as it were, into the finn
. Animal physiology. Physiology, Comparative; Physiology, Comparative. GENERAL STRUCTURE OF FISHES. 83 nishing the resistance which it offers to their progress, and of increasing the extent of the oar-like surface, by the stroke of which the body is propelled forwards (Chap. xn). 99. The preceding figure of the skeleton of the Perch shows the bony apparatus, by which this extended surface is supported. The spinous processes of the vertebrae, which pro- ject upwards from the vertebral column, are long, and are con- nected with another set of bones, which continue them, as it were, into the finny expansion that rises from the back, of which they constitute the framework. There is a corresponding series of bones below ; but they leave a part of the trunk free, to contain the viscera. They form another fin behind, however; and they spread out at the tail to support its large expanded surface. It is, therefore, by bending its spinal column, that the side stroke of the tail and of the hinder part of the body, is made, for the propulsion of the fish through the water; and thus, in this lowest group of the vertebrated series, the act of motion is per- formed by the vertebral column itself, instead of being committed to the limbs as in Birds and Mammalia. But these limbs or members are not altogether wanting in fishes; for there are usually one or two pairs of fins (those already mentioned are single, and are placed on the central line of the body) which evidently represent the arms and legs of man. The hinder pair of these is not unfrequently situated nearly as far forwards as the other; this is the case in the perch, as well as in the mullet, of which a sketch is given in fig. 36. The single fins arranged on the central line, are the first and second dorsal, d 1 and d 2, the caudal or tail-fin, c, and the anal fin, a; at v is seen one of the ventral fins, which correspond to the legs; and above this is shown one of the pecto- _' „ _ 1 Fig. 39—Bearded Mullet. ral fins,
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