on muscular Motion. 
ii 
description r Mr. John Hunter appeared to have had some 
incomplete notions upon this subject, which may be gathered 
from his representation of a materia vitae 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 ani- 
mals, until the body appears to be one homogeneous substance. 
The cavity for receiving the food is indifferently the internal, 
or external surface, for they may be inverted, and still con- 
tinue to digest food ; the limbs or tentacula may be cut off, 
C 2 
