324 Mr. Guthrie 07i the Heart of Test. Indka. 



the left side, this muscle seems wantino;, or is not so well marked, and the 

 ostium through which the blood passes is not so directly downwards, as it 

 is outwards ; so that the blood seems forced against or into the external 

 edge or spongy wall of the left ventricle, from which no vessel is given off. 

 Three arteries arise from the right ventricle at its upper and anterior part, 

 the veins all entering the auricles from behind (the animal being exa- 

 mined on its back.) The pulmonary artery is the lowest, the two Aortm 

 in succession one immediately above the other. Each of the three ves- 

 sels is furnished with two semilunar valves, like the semilunar valves of 

 these vessels in the human subject. The pulmonary artery is as large as 

 the two Aortas, and divides into two about an inch and a half from its 

 origin. The superior of the two Aorta is on a level with the under edge 

 of the valve of the auricle. The cavity of each ventricle is lined by a 

 fine membrane, v/hich marks its extent ; at the inferior part, several ten- 

 dinous cords pass across from behind forwards diagonally, diminisaing the 

 size of the passage from one ventricle to the other. When the right ven- 

 tricle is opened from behind (considering the belly of the animal as the 

 front), a strong muscular band covered by this smooth memirane, and 

 to which some of these tendinous cords are attached, (the pulmonary 

 valve before alluded to) , is seen passing from the point of the lower edge 

 of the heart across to the right anterior part of it, just abov« the orifice 

 of the pulmonary artery, and to the commencement of the Aortic open- 

 ings. This appears to divide, in some measure, the ventrble into two 

 parts, as well as to form with the tendinous cords a sort of imperfect 

 septum between the two sides of the heart. On attentive coisideration, its 

 use seems to be, to force the venous blood on the (ontraction of 

 the ventricle, in the first instance, into the pulmona'y artery ; for 

 when the ventricle and it contract together, it closes u3 that part in 

 which the pulmonary artery is situated, and cuts off tbe^ommunica iDn 

 between it and the upper part of the ventricle, into whfh the scarlet or 

 arterial blood is now passing through the ■ pening in fie septum. At 

 the same time that the contraction of this fleshy colujin closes up the 

 passage into the pulmonary artery, it draws the aortic ofenings more di- 

 rectly opposite to the passage through the septum from he left ventricle, 

 which is also diminished by the tendinous cords alreaci" alluded to ; so 

 that no admixture of arterial or scarlet, and black or enous blood takes 

 place in regard to the pulmonary artery, although it mpt occur in regard 



