. The development of the chick; an introduction to embryology . Fig. 197. — Photograph of transverse section through a chick embryo of8 o. m., Omphalomesenteric artery. Du., Duodenum. Giz., , Gonad. II., Ihum. M. D., Miillerian duct. Pc, Pancreas. V. umb.,Umbilical vein. It should also be noted that the absence of rotation of thechicks stomach (as contrasted with mammals) and the lesserdevelopment of the great omentum appear to be the causes ofthe more primitive position of the spleen in birds as contrastedwith mammals. CHAPTER XII THE LATER DEVELOPMENT OF THE VASCULAR SYST
. The development of the chick; an introduction to embryology . Fig. 197. — Photograph of transverse section through a chick embryo of8 o. m., Omphalomesenteric artery. Du., Duodenum. Giz., , Gonad. II., Ihum. M. D., Miillerian duct. Pc, Pancreas. V. umb.,Umbilical vein. It should also be noted that the absence of rotation of thechicks stomach (as contrasted with mammals) and the lesserdevelopment of the great omentum appear to be the causes ofthe more primitive position of the spleen in birds as contrastedwith mammals. CHAPTER XII THE LATER DEVELOPMENT OF THE VASCULAR SYSTEM. I. The Heart. (For an account of the earlier development, see Chapters V and VI.) At the stage of seventy-two hours (Fig. 198), the ventricleconsists of a posterior transverse portion and two short parallellimbs; the right limb is continuous with the bulbus arteriosus from which it may be distinguished bya slight constriction, and the left limbwith the atrium. The constriction be-tween the latter is the auricular the two limbs in the interiorof the ventricle is a short bulbo-auricu-lar septum separating the openings ofbulbus and atrium into the ventricle. Aslight groove, the interventricular sulcus,that extends backwards and to the rightfrom the bulbo-auricular angle, marksthe line of formation of the future inter-ventricular septum (Fig. 199). The Development of the ExternalForm of the Heart. We have seen thatin the process of development the heartshifts backwards into the thorax. The ventricle undergoes thegreatest displacement, owing to its relative freedom of move-me
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