306 



ZOOLOGY 



SECT. 



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

 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 coimection with 

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

 the ductus Botcdli (d. hot). 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 crmdal 



ijit.car B 



\\ \rea:t.cu.r 



eec.br.s 



ccc.br. a 



Fifi. 953.— Heart and chief arteries of Salamandra. A. larva ; B, adult, af. hr. a. 1 — 4, 

 aflferent braneliial arteries; h.a<i. biiDms aurta-; rar.ijl. carotid labyrinth; r. art. coniis 

 arteriosus ; ('. ao. dorsal aorta ; d. hot. ductus Botalli ; ex. hr. 1 — 3, external gills ; e.rt. car. 

 external carotid; int. car. intei'ual carotid ; I. an. left auricle ; lii<i. lung; pi. plexus, giving 

 rise to carotid labyrinth; ^^ii.l.o,. imlnionary artery; r.nv. right auricle; (•. ventricle. 

 (Altered from Boas.) 



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

 two reyial liortal 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 j'ugukcr to form a 2)recavctl vein. 

 In the adult the anterior portions of the cardinals undergo partial 

 atrophy, becoming reduced to two small azygos veins (C'cc/rl. i^ost.) 

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

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

 the i^ostcaval ( 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 (Ahd. V.) and joins the hepatic portal, its blood, after 



