TIIK ClHCVLATOn Y .1 /'/' I HATV8. 



of tho blood canal that is tho veins: it in named the auricle. The interim- 

 origin to the divergent or centrifugal part of tho same canal, and is 

 the ventricle. 



Tho cavities of tho heart aro distinguished into riijJit or anterior, and 

 /-/'/ or posterior, because of their relative positions. There are, then : a 

 rijltt auricle and <v////-/V/<-, the two dark-blood pouches; and o,lcft um '!< 

 and ventricle, situated on tho track of tho rod-blood canal. 



Situation. Tho heart, enclosed as it is in a fibro-serous sac, named tho 

 pericardium, is placed in the chest between tho two layers of the mediastinum, 

 opposite the third, fourth, fifth, and sixth ribs; in front of the diaphragm, 

 which separates it from tho abdominal viscera ; above tho sternum, which 

 appears to support it ; and beneath tho vertebral column, to which it is 

 suspended by means of tho largo vessels. (Between the middle of the 

 anterior border of tho heart, in front, and tho entrance to the chest, is au 

 interval of about four inches ; and behind, at the same level, this organ is 

 at a similar distance from the diaphragm. It is distant from the fifth and 

 sixth dorsal vertebrae, from which it is suspended, about 4^ to 5 inches 

 in an average-sized Horse.) 



Form and direction. Tho heart presents the form of an inverted cone, 

 slightly depressed on each side, and whose axis, directed obliquely 

 downwards and backwards, deviates a little to tho right at its superior 

 extremity. 



Volume. In a middle-sized Horse, tho greater axis of tho heart is about 

 1(H inches in length ; its an tero -posterior diameter, measured near the base, 

 is equivalent to about 7 inches. Its lateral diameter does not exceed 

 from 5 to 5 inches. 



Capacity. It is very difficult, if not impossible, to obtain tho exact 

 capacity of tho heart's cavities. From reasoning, one is led to think that 

 the two hearts have exactly tho same capacity, and that this capacity is 

 equivalent to an average of 1 to 1J pints. The amount obtained by 

 measurement is much more considerable; but then the heart is distended 

 to a greater degree than in its physiological state. 



Weight. The weight of the heart varies with the size of animals, and 

 that to a considerable degree. Its average is about G% pounds. (The volume 

 and weight of the heart are very much greater in well-bred than in under- 

 bred Horses. Its dimensions and capacity are greater in the living than 

 the dead animal ; as, after death, its cavities contract, particularly tho aortic 

 ventricle, whose walls are tho thickest. This ventricle will then scarcely 

 contain more than 3-4ths to lith gills ; tho pulmonary ventricle, which 

 is not so thick, and consequently less contracted, may usually receive doublo 

 that quantity ; while in animals experimented on when expiring, it was 

 observed that these two ventricles were much more capacious, and that each 

 contained at least from 1^ to 1 pints.) 



External Conformation of the Heart. (Figs. 258, 259.) 



Tho cone represented by tho heart is divided by a horizontal groove into 

 two unequal portions: tho one superior, comprising tho auricles or auricn/.n- 

 mass ; the other inferior or principal, formed by tho ventricles or r<-ntri,-nl,t,- 

 mass. 



A. VENTBIOOLAB MASS. It is this which determines tho conical shape 

 of the heart, and constitues its largest portion. Owing to tho slight flatten- 

 ing which depresses tho organ in a lateral sense, it may bo considered as 



i 



