i ih-d u thin muscle, nine inches long, situated between the pericardium 

 and the diaphragm of tho Horse.) 



6. Action of tJi i Hotrt. 



The function of the heart is to maintain the circulation of the blood, by 

 the rhythmical contractions of its two pouches. The right pouch sends 

 that fluid to the lungs, whence it returns to the left pouch, and from 

 this it is thrown into all parts of the body, and is brought back again to the 

 right heart. These contractions take place simultaneously in the two cardiac 

 compartment^. 



In taking the heart at the moment when it is in a state of repose : t lint 

 is, in the intervals between tho two contractions, we find that its two 

 pouches are being rapidly filled with the blood brought to it by the venous 

 openings. When sufficiently replete, the auricles slightly contract and 

 push a portion of the fluid they contain into t. ventricles : these contracting 

 immediately after, to propel the blood into the a.' rial ramifications. This 

 passage of the blood into the arteries is a necessary consequence of the 

 contraction of the ventricles, as at the moment of this contraction the 

 auriculo-veutricular valves are raised, and so prevent the reflux of the 

 blood into the auricles. This fluid is then forced to enter the arterial 

 oritin-s. whose valves are separated under the impulsive effort communicated 

 to the column of blood. When the heart returns to a state of repose, these 

 valves fall down, preventing the return of the blood into the ventricular 

 cavities ; while the mitral and tricuspid valves subside against the walls of 

 th< se cavities, and thus again allow the passage of blood through the 

 auriculo-ventricular openings. 



By the term systole is designated the contraction of the heart's cavities, 

 and by diastole, the repose or relaxation of its tissue. For each revolution 

 of the heart there is, therefore : 1, The general diastole of the organ, during 

 which the two cardiac cavities are filled by the afflux of venous blood; 

 L'. The xystole of the auricles, the effect of which is the repletion of the 

 ventri'-li s ; 3, The systole of //< i;-,it,-i,-h>x, propelling the blood into the 

 arterial systems; after which conies another period of general diastole. 



DIFFERENTIAL (1IARACTKE8 IX THE HEART OF OTHER THAN SOUPED ANIMALS. 



lu tin- Os, Shfep, and dxil. tin- ventricular mass of the heart is more regularly 

 .1 than in Soli]...!-; it has thru- longitudinal furrows, one of which is accessory 

 and passes behind the left) ventricle. 



In the OJT two smull bones, named bones of thr heart, are found in the sulistanci of 



Ihe aortic zone. The largest i.s in tin; right side, at tho point when- tlu arterinl ring i> 



n{i|o\iia:ited to the auriculo-ventricular zones ; the other, .situated in the left, is }x-rhaps 



not constantly present. The first is triangular in shape, curved to the right, au.l it.- 



baae din-cted upwards. Tin- right fa'v lies againbt the auiiculo-vvntricnlar o|X'iiing : 



lh li it i- ruvi-r.-d by the walls of the aorta at its COIHIIK n<-< UK nt. It is about an inch in 



length. (The Ox's mart averages from about 3J to 4J Ibs., that of tli. She. p from 5$ to 



It in more elongated and |>ointed in Ruminants than in tho Horse or Pig. The 



in Ihe Ox's heart La elongated from before to Ix-himl. flattened laterally :n;d 



1 '. th.- Kit; its surtncc i rough* in d. and its length is Hometimes alxiut '2 iiuMirs. 



'I'll, li-ft, or fn,'ill I*.!!.-, is iiMially iLittrn, ,1 MI each M'!<- ami triangular, one of its j 



)' directed forwards, another I ;u-kwurd, and a third inlet iorly ; its length is about three- 



quarters of an inch when fully developed. Uesiiles the ( >x, a small <T"-- ..' aped l>one is 



found in the heart of the Sheep, Pig, Camel, Deer, Giraffe, and conn -time.- in the Horse. 



k found in the pericardium of tho Ox, at the border of the left auricle, a row of 



villi -iinihtr to those discovered in tho border of the chicken's lj*nrt.) 



lif;irt !' the Pifj resembles thnt of th*> Horse : its direction is a little mmr oblique. 



'_' i 



