164 Mammalia, 



Placing tlie heart before you, with the apex towards you, 

 and this right ventricle to your left, you will observe (1) a 

 large vessel rather to the right of the median line, and arising 

 from the base of the Heart : this is the Pulmonary Artery 

 which conveys venous blood to the Lungs ; (2) a distinct 

 groove crossing the anterior surface of the Heart diagonally 

 from the left centre of the base to a point a little below the 

 middle of the right margin : this groove marks the line of the 

 interventricular* septum and carries the proper nutrient vessels 

 of the Heart, viz. the Coronary arteries and veins, in its 

 channel ; (3) a large vessel immediately posterior to the Pul- 

 monary artery : this is the Aorta which conveys arterial blood 

 to the body generally ; (4) folded ear-like appendages at the 

 base of each ventricle : these are the Auricles ; and (5) a groove 

 between the auricles and ventricles termed the Auriciilo- 

 ventricular Sulcus. 



By the aid of the coloured injection thrown into them 

 it will be well now to trace out the principal branches 

 of the Coronary Arteries. There are normally two Coronary 

 arteries, one arising from the left, and the other from the 

 right sinus of Valsalva (two small internal pouches in the 

 anterior segment of the root of the Aorta) as in Man ; their 

 distribution is, however, different : for in the Sheep the right 

 Coronary Artery takes a short course in the groove between 

 the right auricle and the ventricle, behind the cone at the 

 base of the Pulmonary artery, and then sends off a short 

 branch posteriorly to the auricle, its main stem continuing 

 along the right margin of the Heart : while the left Coro- 

 nary Artery immediately on leaving the Aorta divides into 

 three branchesf, one running along the anterior interven- 

 tricular groove ; the second traversing the left border of the 



* i.e. the Septum, wliicli separates the cavities of the two ventricles. 



t As an abnormality the third branch is sometimes found commencing by a 

 distinct orifice in the left sinus. 



