620 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



As might be expected, race horses have hearts which are larger than the average, both abso- 

 lutely and relatively. In fat subjects the ratio to the body-weight may be about 0.4 per cent., and, 

 on the other hand, it is commonly 1 per cent, or more in light horses which are not fat. 



The following average measurements were obtained in medium-sized hearts : 



Sagittal diameter of base 25 cm. 



Greatest width of base 18 to 20 cm. 



Circumference at coronary groove 65 to 70 cm. 



Distance between origin of pulmonary artery and apex 25 cm. 



Distance between termination of posterior vena cava and apex 18 to 20 cm. 



-^Right 

 alrium 



monary veins 



Pulvionary 

 veins 



Posterior rena cava 

 Left alrium 



Fig. 544. — Base of Heart of Horse with Large Vessels: Dorsal View. Specimen Hardened in situ. 



The Right Atrhim 



The right atrium (Atrium dextrum)^ forms the right-anterior part of the base 

 of the heart, and lies above the right ventricle. It consists of a sinus venarum, 

 into which the veins open, and an auricle^ (Auricula dexter) . The latter is a conical 

 diverticulum which curves around the right and anterior surfaces of the aorta, its 

 blind end appearing on the left side in front of the origin of the pulmonary artery ; it 

 is the most anterior part of the heart. 



There are five chief openings in the right atrium. The opening of the anterior 

 vena cava (Ostium vense cavse cranialis) is in the dorsal part, and is chiefly opposite 

 to the fourth rib. The opening of the posterior vena cava (Ostium venae cavse 



'■ Also termed the right auricle. ^ Also termed the auricular appendix. 



