600 ANATOMY AND PHYSIOLOGY OF THE HORSE^S FOOT. 
this circle, but allowed to maintain its communications with 
the bone, it would receive from the interior of that phalanx 
all the elements necessary to sustain its vitality. Even if 
isolated from both the coronary circle and the surface of the 
bone to a considerable extent, but in continuity with them at 
some point, it would yet obtain from this small source enough 
blood to ensure its maintaining its health and exercising its 
functions. 
The same may be said of the important membrane covering 
the sole of the bone ; this can live when separated from 
everything but its connection with the os pedis, and vice versa , 
if allowed to remain attached even by a shred. 
In the normal state, then, there is an intimate vascular 
unity between the various parts of the foot, while at the same 
time, as if to compensate for, or be prepared to meet, the acci- 
dents to which such a peculiarly constructed organ is liable, 
each part is capable of isolation and independent vegetation ; 
one branch or trunk can take up the duties of another in 
addition to its own, and where both are incapacitated by 
accident or disease, the more minute divisions or ramuscules 
can again supplement these, and carry on the circulation 
uninterruptedly. 
In other animals, under certain conditions, we find a similar 
arrangement of the arteries, evidently with the object of 
breaking the force of the current of blood by dispersing its 
volume into a number of smaller channels, which retain it 
sufficiently long for the purpose of nutrition, and yet prevent 
its accumulating in too great quantity in organs that might 
suffer from congestion. We have an admirable example of 
this in what is called the “rete mirabile” of Galen, a won- 
derful breakingmp of the carotid and vertebral arteries at 
the base of skull of creatures, which, in grazing, are com- 
pelled to keep their heads in a dependent position for a long 
time ; this plexiform arrangement is accordingly most largely 
developed in grazing animals, less in those which browse, 
and least of all in the giraffe, which usually feeds with the 
head elevated. It is also a very marked feature in the dispo- 
sition of the brachial and femoral arteries of sloths and 
slow-lemurs, animals with long prehensile limbs, which have 
great freedom and extent of motion, and yet which, by this 
sudden breaking-up of these vessels into an innumerable 
multitude, can enable these creatures to remain suspended by 
one or both limbs for hours. It is the same in the legs of 
the goose, swan, and other birds which are accustomed to 
stand for long periods on either one or both legs; and in the 
whale family ( Cetacea ) there is an extreme degree of plexiform 
