. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. l82 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. exception of one feature in the amniotes. In these, as a result of the great size of the yolk, the heart at first appears as a pair of widely separated tubes (Fig. 195J, which later approach and then unite to form the single tube, which then undergoes the twist- ing and differentiation already described. The ventral aorta extends for- ward from the heart beneath the pharynx. It is a part of the same primitive tube from which the heart arises. From this tube there are given off ves
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. l82 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. exception of one feature in the amniotes. In these, as a result of the great size of the yolk, the heart at first appears as a pair of widely separated tubes (Fig. 195J, which later approach and then unite to form the single tube, which then undergoes the twist- ing and differentiation already described. The ventral aorta extends for- ward from the heart beneath the pharynx. It is a part of the same primitive tube from which the heart arises. From this tube there are given off vessels — right and left —- Taortic arches) which pass outward in the tissue between the gill slits, then up on either side of the pharynx, and at last those of each side unite dorsally to form a vessel (radix aortae) above the pharynx. Behind the region of the gill slits the radices of the two sides unite to form a tube ^dorsal aorta), running back- ward between the notochord fver- tebral column) and the alimentary canal to the end of the body. From these arterial vessels smaller arteries are given off to Fig. 196. Diagram of early supply the various regions of the arterial circulation, a, auricle; an, , , t^ anterior abdominal artery; *, bul- ^ody. From the first Or antCnOr bus arteriosus; c, conus arteriosus; ca, caudal artery; ci, common iliac artery: col, coeliac axis; ct, carotids; d, dorsal aorta; f, femoral arterj'; z, iliac artery; im, inferior mesenteric arteries; j, jugular vein; ot, metameric Tintercostal) arteries; o, omphalomesaraic (hepatic) veins; /, postcardinal veins; ra, radix aortae; j, sinus venosus ; sc, subclavian artery; :m, superior mesenteric artery; v, ventricle; va, ventral aorta; ;/, vertebral Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterlin
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