THORAX AND ABDOMEN OF THE HORSE 



35 



The papillary muscles are two in number and large in size. 

 Trabeculae carnese are less conspicuous than in the right ventricle. 

 The valve (valvula bicuspidalis) guarding the atrio-ventricular orifice 

 has two cusps, larger and stronger than the segments of the tri- 

 cuspid valve, and cranial and caudal in position. The caudal cusp 

 lies bet\veen the atrio-ventricular orifice and the opening into the 

 aorta. 



A. coronaria dextra 



A. pulmonalis. - 



A. coronaria 

 sinistra. 



Aorta. 



Right atrio-ventricular 

 orifice. 



V. cordis media. 



-- :^ - Coronary sinus. 



Left atrio-ventricular 

 orifice. 



V. cordis magna 



Fig. 16. — Transverse section of the heart at the level indicated by the 

 line A in Fig. 15. 



Blood leaves the left ventricle by an opening (ostium aorticum) 

 leading into the aorta, round which there are three semilunar valves 

 similar to those guarding the entrance into the pulmonary artery, 

 but stronger in order to support a greater pressure of blood. These 

 will be examined later. 



A. PULMONALIS. — The pulmonary artery is the large vessel that 

 leaves the conus arteriosus of the right ventricle. The first part of 

 the artery lies between the apices of the auricles of the right and 



