Metasoa Rana. 



28 S 



FIG. 148. ARRANGEMENT OF THE CHIEF ARTERIES 



AND VEINS IN THE FROG. (Owen.) 



of the ccelom. The heart is enclosed in a double-walled 

 sac, or pericardium, between the walls of which there is a 

 space filled with a colourless nutritive fluid known as lymph. 

 From and to the heart a number of large blood-vessels 

 pass, dividing 

 afterwards into 

 smaller branches. 

 The heart itself 

 is subdivided into 

 three chambers, a 

 ventricle, which 

 composes the apex 

 and aconsiderable 

 portion of the 

 body, and two 

 auricles, which 

 occupy the base 

 of the pyramid. 

 The heart lies 

 close to the ven- 

 tral body- wall in 

 such a way that 

 the apex points 

 backwards and the 

 large vessels arise 

 from near the base 

 and pass forwards. 

 Above or behind 

 the heart . lies a 

 large membranous 

 sac known as the 

 sinus venosus, 

 into which all the 

 impure blood is poured in the course of the circulation ; 

 below or in front of the heart and springing from the 

 ventricle is a large muscular vessel known as the truncus 



H, heart ; A, above the origin of the common carotids ; 

 p, the left lung ; /, pulmonary vein ; p', pulmo- 

 cutaneous artery ; o, right precaval vein ; /, hepatic 

 vein ; L, portal vein ; v, postcaval vein ; A, union 

 of the two aortae ; u, right aortic arch ; k, renal vein ; 

 /', renal artery ; , anterior abdominal vein ; A', divi- 

 sion of the aorta into two common iliac arteries going 

 to the hind limbs. Compare this figure with fig. 53. 



