130 



THE ANATOMY OF THE HORSE. 



papillares, each with its set of chordfe tendinsEe, and three large cusps ; 

 but it will be observed that one set of the chorda; tendinete does not 

 pass entirely to one cusp, but divides itself between two adjacent 

 segments. 



Directions. — A better view of the tricuspid valve may now be obtained 

 by cutting through the auriculo-ventricular ring near the point where 

 the first incision was begun in opening the ventricle, selecting the 



"When some of the chordse tendinese have 

 the wall of the ventricle to be thrown 



interval between two cusps, 

 been cut, this will enable 

 outwards. 



When the ventricle contracts, the blood, prevented by the tricuspid 

 valve from passing back into the auricle, is forced upwards into the left- 

 anterior portion of the ventricle, and leaves the cavity by the pulmonary 

 artery. This portion of the cavity, which leads up to the artery, is 



termed the conus arteriosxis,. The orifice 

 of the 'pulmonary artery is surrounded 

 by a valve composed of three creseentic 

 segments, and hence termed the semi- 

 lunar valve. The convex border of each 

 segment is fixed to the wall of the artery 

 where it springs from the ventricle. The 

 concave border is free, and shows at its 

 mid point a minute, fibro-cartilaginous 

 thickening — the nodiihis or corpus 

 Araniii. On each side of the corpus a 

 small creseentic portion near the free 

 edge of the segment, and distinguished 

 from the rest by its thinness, is termed 

 the lunula. One surface of the valve 

 is convex, and, during contraction of 

 the ventricle, it is directed to the blood- 

 stream ; the other is concave, and directed 

 to the wall of the artery, which, opposite 

 each segment, forms a pouch — the sinus 

 of Valsalva. When the ventricle has 

 ceased to contract, the elastic recoil of 

 the artery forces the blood against the 

 concave side of the segments, and carries 

 them inwards till they meet and com- 

 The blood is thus propelled along the 

 pulmonary arteries to the lungs, where, in the capillary plexus on the 

 walls of the air-cells, it is purified. The purified fluid is then carried 

 from the lungs by the pulmonary veins, which pour it into the left 

 auricle of the heart. 



Fig. H. 



Diagram of thk two Cavities of 



THE LEFT SIDE OF THE HeART (Etlis). 



/.■. Left pulmonary veins ; i. Right 

 pulmonary veins ; o. Remains of fora- 

 men ovale ; /. Left auriculo - ventri- 

 cular opening ; ni. Auricular appendix ; 

 n. Aperture of the aorta. 



pletely close the opening. 



