CAMELS WITH SOUTH AFGHAN EXPEDITION, 1878-9. 705 
the trachea or windpipe, consisting of a number of cartilagi¬ 
nous rings, lined by a continuation of the membrane of the 
larynx, the most remarkable peculiarity in the camel being 
the number of pieces, the natural consequence of length of 
neck. This windpipe, on reaching the chest, bifurcates, 
one branch going to each lung; each branch is again 
divided and subdivided, until it gradually loses its cartilagi¬ 
nous character, and becomes membranous only; these are 
called the bronchial tubes, and ultimately end in cells com¬ 
posed of so attenuated membrane that the air conveyed 
to them comes into such close approximation to ramifications 
of blood-vessels surrounding them that, by a process called 
endosmose and exosmose, an interchange of gases takes 
place, and the object of respiration is attained, viz. the oxy¬ 
genation of the blood, by which it is endowed with its vivi¬ 
fying principle, and the partial deprivation of the same 
fluid. The lungs, then, are spongy bodies composed of air- 
tubes and cells, blood-vessels, and a tissue, which connects 
the parts together; they are divided into two—right and 
left—which are subdivided into lobes, the peculiarity of 
those of the camel being that this latter division is less 
marked than in most mammalia. The lungs are covered 
with a fine membrane of a serous nature, called pleura, 
which is also reflected upon the inside of the chest, the 
secretion from which performs the office of lubrication, and 
by its means any attrition during the motions of inspiration 
and expiration is avoided. 
The consideration of the pneumonic apparatus would be 
incomplete without a glance at the circulatory. The blood 
being oxygenated as above described, and become of a scarlet 
colour, is carried by veins to the left side of the heart, and 
passing through two of the cavities of that organ, is pumped 
through an artery (the aorta), which immediately divides, 
and is there split up into arteries, which are distributed in 
infinitesimal divisions to every part of the body, terminating 
in fine tubes resembling those which ramify on the air cells, 
where a similar interchange takes place, which is reparative, 
there being a deposit of new material and a removal of the 
effete; the worn-out matter now tinges the blood with 
a deep red colour, it is taken up by the minute veins, 
which, by combining, increase in size and diminish in num¬ 
ber until they terminate in the two main ones (anterior and 
posterior venae cavae), which enter the right side of the 
heart; the blood is pumped through the two divisions of 
that viscus into the artery going to the lungs (the pulmo¬ 
nary), on reaching which, it is again distributed by ramifi- 
lii. 50 
