626 



ANATOMY OF VERTEBRATES. 



4.35 



Draiichial circulatinn ; IniTal Newt {Triton). ccl-.xxxil. 



and activity, the principal circulating vessels present the arrange- 

 ment shown in fig. 435. 



The vessel, ib. 4, originally distinct and large before the deve- 

 lopement of the gills, is now very small, and so close to the 

 origin of 3 as to appear to be its first branch : it anastomoses 

 with the branch 21 from the aortal root of its own side, and 

 proceeds to the nascent lung 19. The artery 3 supplies the hind- 

 most gill, and distri- 

 butes its branches to 

 the several branchial 

 leaflets, 5, where they are 

 resolved into the capil- 

 lary network, fig. 343, 

 ji. 514 ; the blood is re- 

 turned by the branchial 

 veins, fig. 435, 7, 8, to the 

 trunk 9, which at 16 joins 

 the corresponding vein of 

 the middle gill to form 

 the aortal root or arch of 

 that side : this receives 

 the anastomosing vessel 13, from the branchial vein of the first gill, 

 and then sends off the accessory origin, 21, of the pulmonary artery, 

 1 n. The third primary vascular arch, 2, is the branchial artery of 

 tlie middle gill : it effects a small anastomotic communication, 14, 

 with the vein of the gill before proceeding to expend itself upon the 

 branchial lamella;, c ; the returning trunk, 9, after receiving the 

 anastomotic twig, 14, joins the vein, 16, of the third gill to form 

 the aortic arch. The foremost primary vascular arch, i, before 

 going to the first gill, anastomoses by a small channel, 5, with the 

 vein, 9, of that gill ; which vein, after the above anastomosis, 

 sends off the vessel 1 1 to the head : before the anastomosis it 

 passes back and di^■idcs into the vessel 13, joining the beginning 

 of the aortal arch, and the recurrent branch 12, which also conveys 

 arterialised blood to the head. 



As absorption of the branchia3 proceeds in the jn'ogressing 

 metamorphosis, the following changes are observed in the above 

 described vessels, fig. 43G : the anastomosing channel, s, between 

 the roots of the artery and vein of the first gill, dilates as the cir- 

 culation through that gill is checked, and sends more blood into 

 the artery 11, into the anastomotic channel 13, and into the arterv 

 1 L'. In like manner the lilood of the second gill begins to be diverted 

 liy the anastomotic t'luuuiel asi(sl)ase leading to ic, which assumes 



