THORAX AND ABDOMEN OF THE HORSE 27 



convex and crossed obliquely by a furrow, the right longitudinal groove 

 (sulcus longitudinalis dextra), that begins at the coronary groove and 

 ends on the caudal border of the heart close to the apex. The groove 

 divides the surface into two areas, of which the more cranial, formed by 

 the right ventricle, is about twice as extensive as the caudal area, formed 

 by the left ventricle. 



■" Vena cava cranialis. 



Truncus brachiocephalicus. --^ — 



A. pulmonalis. 

 Ligamentum arteriosum. - 



Aorta. -*-/■— 

 Left atrium. 



"-^^^ Vv. pulmonales. 



Fig. 11.— The base of the heart with the great blood- ves.«els. 



Like the right, the left surface of the ventricles is convex and 

 crossed by a groove, the left longitvdinal groove (sulcus longitudinalis 

 sinistra). But the left groove is nearer the cranial border of the heart, 

 so that the caudal two-thirds of the surface is formed by the left 

 ventricle, while the cranial third is occupied by the right ventricle. 

 The left longitudinal groove begins at the coronary sulcus immediately 

 caudal to the origin of the pulmonary artery, and ends on the cranial 

 border of the heart a short distance from the apex. 



From the circumstance that the longitudinal grooves mark the 

 position of the interventricular septum, and that neither reaches the 



