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ARATOMYY cn 67 
breathe. Division, into right and left lung; the right has three 
lobes, the left only two. They are connected wilh ae and 
heart. Substance, full of air cells, and vessels for air and blood, 
connected together by a spongy and cellular substance.” It has an 
ernal membrane from the pleura. Its nerves are from the eighth 
ir and great rib. Lymphatics are to be seen’ on its external sur- 
face. Its glands are, large blackish glands about the windpipe. 
Use, for respiration, voice, and making of blood. PU Oth es 
PHYSIOLOGY OF RESPIRATION. 
Respiration, or breathing, consists of inspiration, or the in, 
of air into the lungs, and expiration, or the egress of ‘the air 
; 
the lungs Sas ain he Sarge ace > ia¥ 
or diminished according to our will, it is termed voluntary. 'The 
exciting cause of inspiration is the air rushing into the lungs and 
irritating its nerves, which irritation is, by consent of parts, commu- 
nicated to the diaphragm and rib muscles, and compels them to con- - 
tract. ‘This contraction and the pressure of the elastic air, therefore, — 
dilate the chest. The air being deprived of its stimulus, the fib 
_ branches of the lung artery form a beautifal ne re 
the internal surface of the air cells. During expiration, the a 
‘séls ‘are collapsed ; consequently. the blood vessels become trooked, 
and the blood is prevented from passing. In inspiration, then, the 
air cells being dilated, the crooked vessels are elongated and a free 
passage afforded to the blood : the very delicate coats of these vessels 
are also rendered so thin as to suffer a chemical action to take place _ 
between the air in the cells and the blood in the vessels. Thiscon- ~ 
stitutes the principal use of respiration, viz.: the blood absorbing the _ 
orygen from the atmospheric air, by which the nervous energy is in- _ 
ereased and vital heat generated. O° ee OO tan eile = 
state; and thus the ‘air is expelled from the vatiticeaady 
+ 
COVERING OF THE HEART. 
A membranous bag surrounding the heart : adhering to the dia- 
phragm, ph breast bone, cartilages of the ribs, gullet, descend- __ 
in tam, andthe veins and great arteries going to and fromthe __ 
heart. Use, to contain the heart, and to separate a fluid, which may 
Jubricate and prevent it from growing to this membrane. — 
THE HEART. 
A muscular viscus situated in the cavity of the above 
which serves for the motion of the blood. It is divided 
