description: Mr. John Hunter appeared to have had some incomplete notions upon this subject, which may be gathered from his representation of a materia vitæ in his Treatise on the Blood, &c. Perhaps it Would be more proper to distinguish the peculiar matter of muscle by some specific term, such, for example, as materia contractilis.
A particular adaptation for the nerves which supply the electrical batteries of the torpedo, and gymnotus, is observable, on the exit of each from the skull; over which there is a firm cartilage acting as a yoke, with a muscle affixed to it, for the obvious purpose of compression: so that a voluntary muscle probably governs the operations of the battery.
The matter of the nerves, and brain, is very similar in all the different classes of animals.
The external configuration of animals is not more varied than their internal structure.
The bulk of an animal, the limitation of its existence, the medium in which it lives, and the habits it is destined to pursue, are each, and all of them, so many indications of the complexity or simplicity of their internal structure. It is notorious that the number of organs, and of members, is varied in all the different classes of animals; the vascular and nervous systems, the respiratory, and digestive organs, the parts for procreation, and the instruments of motion, are severally varied, and adapted to the condition of the species. This modification of anatomical structure is extended in the lowest tribes of animals, until the body appears to be one homogeneous substance. The cavity for deceiving the food is indifferently the internal, or external surface, for they may be inverted, and still continue to digest food; the limbs or tentlacula maybe cut off,
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