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 idiameteriot bases fai cst. a. ac .cciae naman cients 
Greatest width of base... .... SOR hn: Raat 1S to 
Circumference at coronary groove ee a res 
Distance between origin of pulmonary artery and apex 
Distance between termination of posterior vena cava and apex. 
| 
! 
= 
Pulmonary 
AS 
veins Left atrium 
Fic, 544.—Base or Heart or Horse with LarGe Vessets: Dorsar Virw. 
THE RIGHT ATRIUM 
The right atrium (Atrium dextrum)! forms the right-anterior part of the base 
It consists of a sinus venarum, 
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 
of the heart, and lies above the right ventricle. 
into which the veins open, and an auricle? (Auricula dextra). 
is the most anterior part of the heart. 
There are five chief openings in the right atrium. 
1 Also termed the right auricle. 
. .65 to 
_.18 to 
\ Posterior vena cava 
SpreciMEN HARDENED in situ, | 
The opening of the anterior 
vena cava (Ostium ven cave cranialis) is in the dorsal part, and is chiefly opposite 
to the fourth rib. The opening of the posterior vena cava (Ostium ven cave 
2 Also termed the auricular appendix. 
25 cm. 
20 em. 
70 cm. 
25 em. 
20 em. 
~~~ Right 
atrium 
Pulmonary veins 
