222 



THE VASCULAR SYSTEM. 



Arteries arid veins of the Truncus 

 arteriosus of Bufo vulgaris, after 

 Hyrtl. 



a Arteria bulbi. 



b Truncus arteriosus. 



h, i Hepatic portal veins. 



t Riglit and left synangium. 



v Vena bulbi anterior. 



vi Left innominate vein. 



re Vena bulbi posteiior (V. cardiaca). 



A Right auricle. 



A' Left auricle. 



V Ventricle. . 



(endocardium), which covers the various 

 trabeculae ; the external surface of the 

 heart is likewise covered with an epi- 

 cardial layer of endothelium (Fig-. 138 



E}.-\ 



e. The blood-supply to the heart. 



With the exception of the truncus 

 arteriosus, no part of the heart possesses 

 blood-vessels (Hyrtl). [The truncus 

 arteriosus (Fig-. 142 b} has a rich anas- 

 tomosis, which receives its blood by 

 the arteria bnlbi (a), a branch of the 

 carotid arch. Two veins connect this 

 anastomosis with the systemic veins, 

 and with the hepatic portal veins : the 

 former, vena bulbi anterior (v), passes 

 over the auricles to open into the left 

 innominate vein (vi] ; the latter, the 

 vena bulbi posterior (vc] or vena car- 

 diaca, as it is more usually named, passes 

 from the tr/mcitx arferioxm in a fold 

 of pericardium, and then courses back- 

 wards to open into the anterior-abdo- 

 minal vein.] 



II. THE ARTERIES. 



(The original arrangement of this section has been modified. 1 ) 



The Truncus arteriosus divides to form two vessels (Figs. 132, 

 1 34) ; each of these is divided by two partitions into three com- 

 partments, which after a short course together separate to form 

 three distinct vessels, the carotid, systemic, and pulmo-cutaneous 

 arches. 



1. The carotid arch (Canalis carotico-lingualis, Briicke ; 

 caroticufs), (Fig. 143 /) is the most anterior of the three arches : it 

 winds round the side of the oesophagus as far as the carotid gland, 

 where it divides to form two branches ; the right carotid arch gives 

 off a small branch to the Truncus arteriosus, the Arteria bulbi (see 

 above). 



