Lectures on the comparative anatomy and physiology of the vertebrate animals Volume 2 - Tapa blanda

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1846 Excerpt: ... currents rush out at the open posterior branchial orifices. These functions are the true condition of the high development of the os hyoides in fishes. I have noticed the great development, the persistence, and ossifi cation of the branchial arches in connection with the transitory manifestation of cartilaginous branchial arches in the larvae of the Batrachia: this is one of those similarities that has led to the metaphorical expressions of " gigantic tadpoles," as applied to fishes. But we see how admirably the branchial arches are adapted to the aquatic respiration of the fish, by their advance to a grade of development, which they are never destined to attain in the frog. Observe their firm ossification, their elastic joints, the sieve-like valves developed from the side next to the mouth, pre-arranged with the utmost complexity and nicety of adjustment to prevent the entry of any particles of food or other irritating matters into the interspace of the tender, highly vascular, and sensitive gills. Observe, also, how the last pair of these arches is reduced to the capacity of the pharynx which it surrounds, how it is thickened in order to support teeth of multiform character, according to the nature of the food; in short, converted into an accessory pair of jaws, and the most important of the two. In no other Vertebrate Animals is the mouth provided with maxillary instruments at both fore and hind apertures: in no other part of the ichthyic organisation is the special divergence from any conceivable progressive scale of ascending structure culminating in Man so plainly marked as in this. All writers on Animal Mechanics have shown how admirably the whole form of the fish is adapted to the element in which it lives and moves: the viscera are pack...