184 THE FEOG. 



vein, at the level of the hinder border of the pericardial cavity, 

 to form the Cuvierian vein (Fig. 71). The two Ouvierian veins, 

 right and left, run almost vertically downwards to open into the 

 outer ends of the sinus venosus (Fig. 71). T he Cuvierian vei ns 

 pe rsist as the anterior vense cavee of the frog . 



8. T he inferior jugular veins collect the blood from the floor 

 of the mouth, including the large sinuses above the sucker into 

 which the mandibular and hyoidean veins open (Fig. 78) : they 

 then run back in the side walls of the pericardial cavity, and open 

 into the right and left Cuvierian veins respectively, just before 

 these reach the sinus venosus. 



f. T he posterior ven a cava is a large median vein (Fig. 76, 

 Vi), which develops shortly after the mouth opening is esta- 

 blished ; it is continuous posteriorly with the hinder portion s of 

 t he two posterior cardinal veins , which unite togeth er ; and , 

 further forwards, it runs in a deep groove along the left side of 

 t he live r (Fig. 71, vh), joins with th e hepatic veins, and then 

 o pens into the sinus ven ojuS;_ The blood from the hinder part 

 of the body ca n now return to the heart either along the poste rior 

 cardinal and Cuvierian vein s, o r^ else by the posterior vena cava. 

 In the later stages of tadpole life more and more of the blood 

 follows the latter course, and the an terior ends of the po sterior 

 cardinal ve ins g raduall v diminish in size, an d durin / j the m eta- 

 mo rphosis disappear comple tely. 



g. The renal portal vein s a re formed by longitudinal anas to- 

 motic communic ations between the transverse, or vertebral, veins 

 of the hinder part of the body ; they are joined posterioi JEjjv the 

 ili ac vein s, and with t hese form the afferent renal system of vevn s. 



h. TtiP an^^vinr a.hflmnTTia.l veiti is at first paired, and is in 

 connection, not with the liver, but the heart. The pair of vessels 

 appear first in the ventral body wall, extending backwards a 

 short distance from the sinus venosus ; they soon extend further 

 backwards, and acquire communications with the veins of the 

 hind legs and of the bladder. At a later stage, the two anterior 

 abdominal veins unite at their hinder ends, in front of the 

 bladder, while further forwards the vein of the right side disap- 

 pears, the left one alone persisting. Later still, the anterior abdo- 

 minal vein loses its direct communication with the sinus venosus, 

 and acquires a secondary one with the hepatic portal veins, or 

 afferent veins of the liver. 



