238 the Ventricles of the Heart. [Book IX. 



The principal part of the mufcular fubftance of the 

 heart forms two cavities called the ventricles. The 

 pofterior or left ventricle of thefe is much thicker, 

 ftronger, longer, and rounder than the other; the an- 

 terior or right ventricle is wider, fhorter, and thinner*. 

 The feptum, or that portion of mulcular fubftance 

 which is placed between the ventricles, feems chiefly 

 to belong to the former, and gives the latter an ap- 

 pearance of being merely an appendage. 



At the bafe of the heart are two cavities, which 

 are each of them divided by anatomifts into two 

 parts, the fmus and the auricle ; but as thefe together 

 form one cavity, it will anfwer bed the purpofe of 

 perfpicuity to fpeak of them fimply by the name of 

 auricles . The auricles are compofed of two mem- 

 branes, with fome mufcular fibres. Like the ven- 

 tricles, they are feparated from each other by a feptum, 

 and one of them obtains the appellation of the an- 

 terior or right auricle, the other that of the pofterior 

 or left. Each of them communicates with the ven- 

 tricle which is placed next it, and which bears 'the 

 fame name. 



Between the auricles and ventricles of the heart are 

 placed valves, as alfo at the mouths of the great 

 arteries, which prevent the blood from paffing in any 

 other than the proper direction. 



The valves, which are placed between each of the 

 auricles and ventricles, are turned inwards towards the 

 latter cavities. The valves, fituated at the entrance 

 of the anterior ventricle, have three remarkable points, 



* The terms anterior and pofterior auric'cs and ventricles of the 

 heart are ufed as defcriptive of the fituauon of them in man. In 

 quadrupeds, the anterior auricle aud ventricle, or thofe which 

 perform the fame purpofe, are placed towards the right fide, and 

 the pofterior towards the left. 



and 



