306 



ZOOLOGY 



SECT. 



arch loses its connection with the dorsal aorta, and becomes tlie 

 carotid trunk ; the second increases in size, forming the main 

 factor of the dorsal aorta, and becomes the systemic trunk ; the 

 third undergoes great reduction, and the fourth becomes the 

 pulmonary artery, its dorsal portion retaining its connection with 

 the systemic trunk in the form of a small connecting branch, 

 the ductus Botalli (d. lot.'). In the Anura, as we have seen (p. 280), 

 the third arch vanishes completely and there is no ductus Botalli. 

 As to the venous system, the Urodela exhibit very clearly the 

 transition from the Fish-type to the condition already described 

 in the Frog. The blood from the tail is brought back by a caudal 



&*" 



FIG. 053. Heart and chief arteries of Salamandra. A. larva ; B, adult, a/, br. a. 14, 

 afferent branchial arteries ; b. ao. bulbus aortse ; car. gl. carotid labyrinth ; c. art. conus 

 arteriosus ; d. ao. dorsal aoi'ta ; d. hot. ductus Botalli; ex.br. 1 3, external gills ; <.'/. <./'. 

 external carotid ; int. car. internal carotid ; 1. an. left auricle ; Ing. lung ; pi. plexus, giving 

 rise to carotid labyrinth ; ynil. a. pulmonary artery ; r. aw. right auricle ; v. ventricle. 

 (Altered from Boas.) 



vein (Fig. 954, Gaud. V.) which, on reaching the coelome, divides into 

 two renal portal veins, one going to each kidney. From the kidney 

 the blood is taken, in the larva, into paired cardinal veins, each of 

 which joins with the corresponding /w#w/r to form aprecaval vein. 

 In the adult the anterior portions of the cardinals undergo partial 

 atrophy, becoming reduced to two small azygos veins (Card, post.} 

 which receive the blood from the region of the back : their posterior 

 portions unite and are continued forwards by a new unpaired vein, 

 the poslcaval (V. cava inf.), which, joined by the hepatic veins, 

 pours its blood into the sinus venosus. The iliac vein from the 

 hind-leg divides into two branches : one joins the renal portal, 

 the other, representing the lateral vein of Elasmobranchs, unites 

 with its fellow in the middle ventral line to form the abdominal 

 vein (Aid. V.) and joins the hepatic portal, its blood, after 



