394 STRUCTURE OF VERTEBRATES. 



DIAGRAM XXIII. 

 Circulatory System. 



Fig. I is a diagrammatic representation of the chambers of, or con- 

 nected with the heart : S. v. the sinus venosus, A. the auricle, V. the 

 ventricle, C. a. the conus arteriosus, B. a. the bulbus arteriosus. (After 

 Wiedersheim. ) 



Fig. 2 represents the typical vascular system of a fish : — H. the heart, 

 c. the cardinaWeins entering it, v.a. the ventral aorta, giving otf afferent 

 branchial vessels {aff. br. ) to the gills, whence efferent branchial vessels 

 ieff. br. ), unite on each side as right and left aortic trunks {R. A., I,. A.). 

 These may unite in front in a cephalic circle (c. c), they give off 

 anteriorly the carotids {ca. ). Posteriorly the arterial trunks unite to form 

 the dorsal aorta {d.a.), from which arteries, e.g. , the coeliaco-mesenteric 

 (c. ;«.), and the renals (^.), &c., are given off. (After Wiedersheim.) 



Fig. 3 represents the five embryonic vascular arches in a Reptile : — 

 ao. the dorsal aorta, ^«/»?. the pulmonary artery, s. cl. subclavian, i.e., 

 and e. c. internal and external carotids. (After Hertwig. ) 



A. B. and C. (after Hatschek) are diagrams of the circulation in Fish 

 (A.), Amphibian (B.), and Bird or Mammal (C). 



H. the heart, g. the gills, Z. the lungs, B. the body. The venous 

 channels are dark, the arterial lighter. The arrows indicate the direc- 

 tion of the flow. 



