. Cunningham's Text-book of anatomy. Anatomy. 1026 THE VASCULAK SYSTEM. , t t c ..i wvi= +l-,o firct aortic arch â and the short ventral limb of the hook, which lies 'n'the'ventr 1 waU of h tig itandthelorsal wall of the pericardium is the primitive ventra m th e Mita â¢U°imejoie j ⢠f the limbilical orifice, that is at its caudal ^^^T^a,^S£. vein, which is carrying blood from the yolk-sac to theTnebcondition described is that found in embryos about 1'4 mm. long, possessing six meso- ^TnlXyos ifwhfoh'the mesodermal somites have increased to fourteen pairs the posterior or cautSpStfonsTo? fl
. Cunningham's Text-book of anatomy. Anatomy. 1026 THE VASCULAK SYSTEM. , t t c ..i wvi= +l-,o firct aortic arch â and the short ventral limb of the hook, which lies 'n'the'ventr 1 waU of h tig itandthelorsal wall of the pericardium is the primitive ventra m th e Mita â¢U°imejoie j ⢠f the limbilical orifice, that is at its caudal ^^^T^a,^S£. vein, which is carrying blood from the yolk-sac to theTnebcondition described is that found in embryos about 1'4 mm. long, possessing six meso- ^TnlXyos ifwhfoh'the mesodermal somites have increased to fourteen pairs the posterior or cautSpStfonsTo? flJ primitive ventral aorta, have fused together to form a single heart (F1 ThePrimitive Heart -The primitive heart lies in the dorsal wall of the pericardium and, T i â¢t S thefirst aortfoarch At this stage the primitive dorsal aortas are still separate wle anoht S each gives off a series of dorsal intersegmental branches and a series of veZa]nbra^ wMA PTss Loss the side walls of the primitive gut on their way to the wall °f ^23Sy situated ventral vessels, as in the earlier stage, ^^s^the ^jtf. Posterior cardinal veins Yolk-sac artery __ (later = superior mesenteric) 2nd aortic arches 1st aortic Anterior cardinal veins Duct of Cuvier Sinus venosus Umbilical arteries Vena umbilicalis impar FIG 320-SCHEMA OF VASCULAR SYSTEM OF AN EMBRYO WITH TWENTY three Somites. (Arteries alter Felix, modified.) which the umbilical arteries arise (Fig. 819). When the embryo has attained a length of 2-5 mm., and possesses about twenty- three mesodermal somites, the two primitive dorsal aortas have fused together, from the tenth to the six- teenth somite, forming in the region of fusion a single dorsal aorta, which becomes the descending aorta of the adult. At a slightly later stage the fusion of the two primi- tive dorsal aortse extends caudalwards to the level of the twenty-third somite, where one of the ventral branches of each primitive vessel becomes enlarged ^-^ of ^^^S
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectanatomy, bookyear1914
