Volume 1

Animal and vegetable physiology, considered with reference to natural theology / by Peter Mark Roget.

  • Roget, Peter Mark, 1779-1869.
Date:
1867
Catalogue details

Licence: Public Domain Mark

Credit: Animal and vegetable physiology, considered with reference to natural theology / by Peter Mark Roget. Source: Wellcome Collection.

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    of the nostrils, which is placed there, to'the surface of the water.* Another peculiarity of conformation, in which the ce- tacea differ from fishes, and which has also an obvious re- lation to their peculiar mode of breathing, is in the form of the tail, which, instead of being compressed laterally, and inflected from side to side, as in fishes, is flattened horizon- tally, and strikes the water in a vertical direction ; thereby giving the body a powerful impulsion, either towards the surface, when the animal is constrained to rise, or down- wards, when, by diving, it hastens to escape from danger. All the essential and permanent parts of the skeleton of vertebrated animals, that is, the spinal column, and its immediate dependencies, the skull, the caudal prolongation, and the ribs, are found in that of the Cetacea. The thorax is carried very much forwards, especially in the whale, and the neck is so short as to be scarcely recognisable ; for the object of the conformation is here, as in fishes, to allow free scope for the movements of the tail, and ample sjeace for the lodgment of its muscles. Tor the purpose of giving greater power and more extensive attachment to these muscles, the transverse processes of the dorsal and lumbar vertebras are expanded both in length and breadth ; and being situated horizontally, they offer no impediment to the vertical flexure of the spine. For the same reason the ribs are continued in a line with the transverse processes, and articulated with their extremities; thus giving still further breadth to the trunk. As there is a total absence of hinder extremities, so there is no enlargement of any of the vertebrae corresponding to a sacrum : and the caudal vertebrae are uninterrupted con- * The substance called Spermaceti is lodged iu cells, formed of a cartilaginous material, situated on the upper part of the head of the Cachalot.