222 



THE VASCULAE SYSTEM. 



Arteries and veins of the Truncus 

 arteriosus of Bufo vulgaris, after 

 Hyrtl. 



(endocardium), wliicli covers the various 

 trabeculae ; the external surface of the 

 heart is likewise covered with an epi- 

 cardial layer of endothelium (Fig*. 138 



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 hdhi {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 hulhi anterior {v), passes 

 over the auricles to open into the left 

 innominate vein (vi) ; the latter, the 

 vefia hulhi jjosterior [vc) or vena car- 

 diaca, as it is more usually named, passes 

 from the truncus arteriosus 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. > 



The Trnncus arteriosus divides to form two vessels (Fig-s. 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 ; JDucfus 

 caroticus), (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 liulhi (see 

 above). 



