216 GENERAL REMARKS UPON THE HEART. 



form obtuse angles with the trunks from which they proceed. 

 In the limbs these angles are acute. 



The communication of arteries with each other is termed 

 Anastomosis. In some instances, two branches which proceed 

 in a course nearly similar, unite with an acute angle, and form 

 one common trunk. Sometimes a transverse branch runs 

 from one to the other, so as to form a right angle with each. 

 In other cases, the two anastomosing branches form an arch, or 

 portion of a circle, from which many branches go off. 



By successive ramifications, arteries gradually diminish in 

 size, until they are finally extremely small. 



The small arteries do not carry red blood, their diameters 

 being smaller than those of the red particles of that fluid, the 

 serous or aqueous part of the blood can, therefore, only pass 

 through them. 



Many of the arteries which carry red blood, and of the 

 last mentioned serous arteries, terminate in veins, which 

 are in some respects, a continuation of the tube reflected back- 

 wards.* 



Position of the Heart. 



— The heart is situated mainly between the sternum and 

 spine ; its left ventricle is placed immediately behind and to 

 the inner side of the left nipple ; its base is horizontal, and 

 nearly opposite a line drawn horizontally from the junction of 

 the cartilage of the third rib with the sternum. The right 

 auricle is placed so that its free border is a little to the right 

 side of the sternum, between the junction of the third and 

 fourth costal cartilages with that bone. The flattened surface 



* Malpighi and Leuenhoek declare, that by the aid of a microscope they 

 have seen arteries terminating in the veins. Haller advances formally his own 

 experience in support of his assertion. Other anatomists have seen, that in 

 blowing into an artery, the air passed into the corresponding veins. Never- 

 theless, Duverney and some others say, that a particular substance is inter- 

 posed between the extremities of these vessels. Ruysch, in his Thesaurus 

 Anatomicus, VI. No. 73, says, in repletione arteriarum, replentur et plurimum 

 quosque venae, et vice versa, ita ut impossible videatur prsecise dicere quomodo 

 res se habeat. Discours sur I'Anat. — h. 



