XXIV] 



CIRCULATORY SYSTEM 



621 



great trunks leaving the two parts of the ventricle communicate. 

 In Birds only one systemic arch remains complete ; this passes 

 round to the right, coming off from the left half of the ventricle ; 

 in Reptiles, it will be recollected, the 

 left fellow of this one was still present. 

 From the systemic arch there arises an 

 innominate artery for either side, sup- 

 plying the trachea, which splits up into 

 a ventral carotid, as in Reptiles, but re- 

 duced as compared with the correspond- 

 ing vessel in them, and into a dorsal or 

 common carotid which supplies the 

 head and a subclavian which supplies 

 the breast and wing. The subclavian 

 artery which arises from the ventral 

 carotid divides into a brachial artery 

 of moderate size for the wing and a 

 very much larger pectoral artery which 

 supplies the pectoral muscles. These, as 

 we have seen, are the real seat of the 

 activities of the wing. The subclavian 

 of Birds corresponds in origin with that 

 of Chelonians and Crocodiles and so is 

 the ventral type of subclavian, as opposed 

 to the dorsal type found in Lizards and 



Amphibians. The arteries supplying the Fm - 311 - Dia S r a m to show 

 , f i arrangement of the prm- 



lungs, the pulmonaries, which, as m O i pa i veins of a Bird. 



the Reptiles, have no longer any con- i. sinus venosus gradually 



nection with the systemic arch, come off 



from the right side of the heart; one 



passes to each side to reach the lungs 



(Fig. 310). The arteries of the hinder 



part of the trunk agree in their general 



arrangement with those of Reptilia and 



Amphibia. In the venous system the 



connection of the two jugulars has been 



already referred to. The jugular joins 



a large subclavian vein to form the 



superior vena cava. The largest part of the subclavian vein, like 



that of the corresponding artery, is made up of a pectoral vein 



returning blood from the pectoral muscles. The front parts of 



10 



10 



disappearing in the higher 

 forms. 2. Ductus Cuvieri 

 = superior vena cava. 

 3. Internal jugular = an- 

 terior cardinal vein. 5. Sub- 

 olavian. 6. Posterior car- 

 dinal, front part. 7. In- 

 ferior vena cava. 8. Renal 

 portal = hinder part of pos- 

 terior cardinal. 9. Cau- 

 dal. 10. Sciatic. 12. Coc- 

 cygeomesenteric. 13. Fe- 

 moral. 14. Anastomosis 

 of jugulars. 



