REVIEW. 
504 
the causes producing them exercise an influence different ac- 
cording to the position they occupy. In this respect the expla- 
nation is incomplete. To resolve such questions as these, we 
must look to some cause beyond this — inquire what establishes 
the analogy between mucous membranes and the part of the 
skin covered by ascending hairs — what that anatomical dispo- 
sition is which, in cows that are the best milkers, places this 
part of the skin in relation with the capacity of the lacteal 
reservoirs. 
We believe that the anatomical disposition established by M. 
Yvart, and the connexion, indicated by it between the long hairs 
and the secretion of milk, is owing to the nerves and sangui- 
ferous bloodvessels. In every region of the body the direction 
of the hair is regulated by that of the arteries ; thus, the hair 
upon the perineum grows from above downward, or from below 
upward, according as the part happens to be supplied by arte- 
ries descending from the pelvis or ascending from the sub- 
pubic region, so that long hairs growing over the udder, the 
thighs, and the perineum, indicate that the mammillary arte- 
ries are continued on to the perineum, after having furnished 
branches to the mammae, and that they are sufficiently nume- 
rous, to impart free activity to the secretion of milk, as is observed 
in cows in which they are most conspicuous ; while the absence 
of such hairs, or the presence of close and short hair, indicates 
that the mammillary arteries, less in number, terminate upon 
the udder ; and that they convey no more blood than is required 
for the nutrition of the gland, and are unable, in the time of 
lactation, to transmit to it blood enough to arouse this function. 
In the first of these cases, where the hairs abound, the mammil- 
lary arteries exceed the muscular; whilst, in the other case, these 
latter are relatively most voluminous: hence comes the differ- 
ence we shall at another time draw attention to in the bulk of 
the muscles of the thigh, and the aptitude of cows to fatten and 
meat for the butcher. 
According to this theory, the longitude of the escutcheon 
ought to signify the activity of the mammse, and, to a certain 
point, indicate the quantity of milk cows give ; notwithstand- 
ing we may imagine that the relation between the surface 
covered by ascending hair and the milk secreted may not be the 
same in ail individuals. It is even probable, supposing the skin 
to be thick, firm and tough, that the arteries supplying the mam- 
mse occupy upon it during foetal existence a smaller space than if 
the skin were thin and fine. In fact, this is precisely what one 
would expect to take place, and Swiss cows, so far from being 
an exception to the Guenon system, confirm it, in shewing it to 
be an illustration of a law of physiology. 
