418 MANUAL OF ZOOLOGY SECT. 



the carotid trunk (car. tr.\ a middle, the systemic trunk or 

 aortic arch^ and an outer or posterior, the pulmo-cutaneous 

 trunk (ptil. cu. tr.). The carotid and systemic trunks 

 communicate separately with the bulbus, the two pulmo- 

 cutaneous trunks communicate with the anterior end of the 

 conus by a single aperture placed just below the free end of 

 the longitudinal valve. 



After being bound together in the way described for a 

 short distance, the carotid, systemic, and pulmo-cutaneous 

 trunks separate from one another. The carotid trunk divides 

 into carotid (Figs. 236, car. a and 237, car.) and lingual (/g.) 

 arteries for the supply of the head, the former having at its 

 base a small swelling, the carotid gland (car. gl.) t consisting 

 of a plexus of blood vessels. The systemic trunks curve 

 round the gullet and unite with one another above it to form 

 the dorsal aorta (d. ao.), from which, or from one of the 

 systemic trunks themselves, the arteries to all parts of the 

 body, except the head, the lungs, and the skin, are given off. 

 The pulmo-cutaneous trunk divides into two, a pulmonary 

 artery (pul.) to the lung, and a cutaneous artery (cu.) to the 

 skin. 



The blood from the head and fore-limbs is returned by 

 veins which unite to form a pair of large trunks, the 

 precavats, which open separately into the sinus venosus. 



One portion of the blood from the hind- limb is carried 

 forward by a vein which unites with its fellow of the opposite 

 side to form the abdominal vein (Fig. 238, abd.\ which passes 

 forwards in the ventral body-wall to the level of the 

 sternum, where it turns inwards and divides into two 

 branches, both breaking up into capillaries in the liver. 

 Just as it enters the liver it is joined by the hepatic portal 

 vein (hp. pt.\ bringing the blood from the stomach, intes- 

 tine, spleen, and pancreas. The rest of the blood from 



