38 Hounds 



As the lungs closely invest the heart extraneous 

 applications ought always to be appUed to the front 

 of the breast in addition to the chest walls. 



(b) Circulatory Apparatus and Circulation of 

 Blood. — Apart from the lungs, the circulatory 

 apparatus comprises the heart, the arteries, veins 

 and capillaries. 



The heart is a hollow, muscular organ constantly 

 contracting and relaxing from birth until death, 

 and this with rhythmical precision, distributing 

 pure blood throughout the body and receiving back 

 impure blood, for distribution to the lungs, to here 

 undergo purification or oxidation. 



The heart of the dog varies in its size and weight 

 in accordance with the variety of dog, being particu- 

 larly well developed in Foxhounds. 



It is enclosed within a membranous sac, known as 

 the pericardium, which consists of two layers, an 

 outer fibrous one and an inner serous one. 



The heart is suspended about the middle of the 

 chest by the large vessels and connective tissue of 

 the mediastinum, the middle of which it occupies. 



The muscular fibres composing the heart are short 

 and have, in addition to transverse stripes, generally 

 small fat granules in the axis of the fibres. Trans- 

 verse stripes are characteristic of voluntary {i.e., 

 under the control of the will) muscular fibres, 

 though the heart is of course involuntary, although 



