THORAX AND ABDOMEN OF THE HORSE 



25 



of the sixteenth bony rib and its cartilaginous segment.^ The apex is 

 opposite the space between the fifth and sixth costal cartilages (or under 

 cover of the sixth cartilage) from 1 to 1-5 cm. from the sternum.^ 



The heart of the horse is slightly flattened laterally, and thus may 

 be described as possessing right and left surfaces (facies dextra, facies 

 sinistra) and cranial and caudal borders (margo cranialis, margo 

 caudalis). 



A. pulmonalis. 



Truncus brachiocephalicus 



Ligamentum arteriosum, 

 V. azygos. 



Aorta. 



Vena cava cranialis 



Auricle of right 

 atrium. 



A. coronaria sinistra 

 (ramus descendens). 



Right ventricle. -\~— — 



Vv. pulmonales. 



Left atrium. 



A. coronaria sinistra 

 (ramus circumflcxus). 



— V. cordis magna. 



- Left ventricle. 



Fig. 9. —The heart and great blood-vessels as seen from the left. 



The exterior of the heart is divided into areas corresponding to the 

 four cavities in the interior. Forming the base are the two atria, 



1 In terms of the cavity of the chest, the base of the heart is a])proximately on a 

 level with the junction of the middle and dorsal thirds of the vertical diameter of 

 the cavity. Though less precise, it may also be said that the base lies about the 

 middle of the vertical diameter of the exterior of the chest taken from the highest 

 part of the withers. 



^ When the horse is standing firmly on all four limbs, the apex of the heart is 

 slightly behind the free end of the olecranon. 



