fact, that even the aorta itself may be gra- ciently shews the minuteness of the lesser 
dually obstructed at some distance from arteries. 
the heart, without the parts which it sup- The secerning arteries are in general too 
plies being deprived of nourishment. From minute to admit of demonstration ; they are 
an attentive consideration of all these cir- however evident in some glands; in the 
cumstances, it has been concluded, that the kidney, for instance, they may be seen con- 
moderate increase of the area of the bran- tinued into the excretory vessels. Subtile 
ches of large arteries ; the acute angles at injections, when thrown" into the larger ar- 
which they divide ; their nearly rectilinear terial trunks, ooze out on the surfaces of 
course ; and the rare occurrence of inoscu- membranes, and into the cellular substance 
lation between them, are designed to faci- and they are generally supposed to be 
litate the rapid motion of the blood in them, poured forth from the open orifices of se- 
so that it may arrive unchanged, and in the cerning arteries. Analogy therefore, ra- 
•same state that it was in when projected ther than actual demonstration, leads us 
from the heart, at that part of the body, for to believe, that the secerning arteries ab- 
the nourishment of which it was intended : stract the particles of nutrition, or the ma- 
whilst, on the contrary, the great increase terials which compose the fabric of the 
of the area of the smaller vessels, the va- body, from the circulating fluids, and de- 
riety of their angles, their tortuous course, posit them from their open mouths, so as 
and their frequent communications were by this means to build up and keep in re- 
designed to check the velocity of the blood’s pair the structure of the body, 
motion, when it has arrived at that part, Distribution of the arteries.— The great 
where secretion is to be performed, and artery, whose branches supply the whole of 
nutrition is to take place. Contrary opi- the body, is named the aorta. It arises 
mons have indeed been maintained ; and from the upper part of the left ventricle ; 
tor the farther discussion of tiiis subject, we and emerges from the heart, between the 
must refer the reader to the remarks on the .pulmonary artery and the right auricle. 
circulation m the article Physiology. It first ascends in the chest ; opposite the 
Termination of the arteries.— When these upper edge of the second rib it bends back- 
vessels have become very minute, they ter- wards till it reaches the left side of the 
minate in two ways; they either turn back spine, in which situation it descends from 
again, and become veins, and return the the fourth or fifth dorsal to the last lumbar 
blood to the heart, or they send off fine vertebra. 
vessels, which abstract something from the By the arch of the aorta is meant that 
circulating blood, and are therefore called part of the vessel, which arises from the 
secerning arteries. Though none but minute heart, and bends across the chest. It sends 
arteries are ever reflected to become veins, off the following branches: the two first 
yet many of them are of sufficient magni- arising at right angles close to the heart ■ 
tude to admit common waxen injection: and the three following from the convexity of 
when tiiis experiment succeeds, the conti- the arch : 
nuity of the arteries and veins is very mani- l. Right coronary artery of the heart. 
fest. It seems therefore to follow from this 2. Left coronary artery of the heart. 
facility of communication, that the mass of 3. Arfceria innominata, a common trunk 
the blood is constantly and freely circulat- dividing into 
ing, in order to undergo that change, which l. Right subclavian. 
is effected in the lungs, whilst but a small 2. Right common carotid. 
part of it proceeds into the very minute ar- 4. Left common carotid. 
teries, for the purpose of having secretions 5. Left subclavian. 
- ■ ' • . ^ ~ rr — ^ uiyuuu uai liiai’C, 
not impart the red colour to the fluid, which without sending off a single branch At 
moves in those vessels. Now, we may ven- this part it divides into the external and in- 
ture to affirm, that these globules do not ternal carotid arteries, the former of which 
much exceed m diameter the 150,000th is distributed to the outside of the head; 
part pt an inch, which circumstance suffi- the latter to the brain. 
