oil muscular Motion. 
7 
the circulation of the blood is not essential to muscular action ; 
so that the mode of distribution of the blood vessels, and the 
differences in their size, or number, as applied to muscles, can 
only be adaptations to some special convenience. 
Another prevalent opinion among anatomists, is the infinite 
extension of vascularity, which is contradicted in a direct 
manner by comparative researches. The several parts of a 
quadruped are sensibly more or less vascular, and of different 
contextures ; and, admitting that the varied diameter of the 
blood vessels disposed in each species of substance, were to be 
constituted by the gross sensible differences of their larger 
vessels only, yet, if the ultimate vessels were in all cases 
equally numerous, then the sole remaining cause of dissimi- 
larity would be in the compacting of the vessels. The vasa 
vasorum of the larger trunks furnish no reason, excepting that 
of a loose analogy, for the supposition of vasa vasorum ex- 
tended without limits. Moreover, the circulating fluids of all 
animals are composed of water, which gives them fluidity, and 
of animalised particles of defined configuration and bulk ; it 
follows that the vessels through which such fluids are to pass, 
must be of sufficient capacity for the size of the particles, and 
that smaller vessels could only filtrate water devoid of such 
animal particles : a position repugnant to all the known facts 
of the circulation of blood, and the animal economy. 
The capillary arteries which terminate in the muscular fibre, 
must be secretory vessels for depositing the muscular matter, 
thelymphasducts serving to remove the superfluous extra vasated 
watery fluids, and the decayed substances which are unfit 
for use. 
The lymphaeducts are not so numerous as the blood vessels, 
