396 EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



names dorsal and ventral (Mackay, 1889) are to be preferred to internal 

 and external, for the latter though in common use are less precise. 



During the development of the young individual there is laid 

 down a general scheme of aortic arches and associated vessels 

 agreeing with that just described, and the processes of modification 

 whereby there becomes evolved out of this the complicated and 

 very different arrangement of the great arteries of the adult a fiord 

 material for one of the most fascinating chapters in vertebrate 



an. d.c. v.c. 



VI 



A. 



l-'i'.. ls7. Illustrating modification of the carotid arteries, correlated 



of the neck region. 



nth elongation 



: i; (,1.,-- .-n:ii...- (/ ,,;;, inn,,tiix) ; p.c, primary carotid. 



<<Mh,-l kit-is ;i, in KJ... I8&) 



A. Pumnid 



emhrv >!..'_> \ . Th.- -j^ncral lines of these processes are best ill ust rated 

 hy an outline of \\hat happens in the ^nmp Reptilia. 



Tin- iiiT.Mi'jviiinit \\hidi the main arteries assume in adult 

 Reptiles shoWfl much variety. The relation which the ad nit 

 ai-!-aii,L r <Mii-nt in tin- more important llc]t ilian types hears to the 

 primitive BCh0nie may he ^aihered IVom an inspect ion n|' Ki^s. ISO. ('. 

 187, A 1- :nnl 1S7.\. ('.' Through the e(ns].i<-i!..ns dilVrrenees in 



1 It must In- n ijieiiiber.-'l ih.-it ii: tln-.irtual .iniiii.il the various l>einls ami tui'iis 

 if tli< i. iin- straii'lileiiril out, !' r example aivh 111 heconies 



a ioriion lit Internal Miotid artery, In the dUgrami the 01 



.tun- ..It lie an Ined l.-r t lie sake of clearnegs. 



