. The development of the chick; an introduction to embryology . ssus pneumato-eutericus sinister. 1. Br.,Left i)ronrhus. Prv., Proventriculus. Hhesin., Recessus hepato-entericus sinister. Rpesin., Right pneumato-enteric recess. Otheral)hreviations as in Fig. 195. According to Choronschitzky, the pcritoiu^al cells invade theneighboiing mes(Michyme, and, spicading through it, form an ill-defined denser area, the fimdamental tissue of which is thereforemesenchymal. The meshes of the latter are in immediate con-tinuity with the \(Mia lienalis, l)Ut the vascular endothelium is. THE BODY-CAVITIES 34
. The development of the chick; an introduction to embryology . ssus pneumato-eutericus sinister. 1. Br.,Left i)ronrhus. Prv., Proventriculus. Hhesin., Recessus hepato-entericus sinister. Rpesin., Right pneumato-enteric recess. Otheral)hreviations as in Fig. 195. According to Choronschitzky, the pcritoiu^al cells invade theneighboiing mes(Michyme, and, spicading through it, form an ill-defined denser area, the fimdamental tissue of which is thereforemesenchymal. The meshes of the latter are in immediate con-tinuity with the \(Mia lienalis, l)Ut the vascular endothelium is. THE BODY-CAVITIES 347 not continued into these meshes. Thus free embryonic cells«f the primordium of the spleen enter the venous circulationdirectly, and become transformed into blood-corpuscles. On account of the intimate relation between the pancreas and spleenin early embryonic stages, certain authors (see esp. Woit) have asserteda genetic connection, deriving the spleen from the pancreas. Thereis, however, no good evidence that the relation is other than that Fig. 197. — Photograph of transverse section through a chick embryo of8 (lays. A. o. rn., Omphalomesenteric artery. Du., Duodenum. Giz., ^on., Gonad. II., Ilium. M. D., Mullerian duct. Pc, Pancreas. V. umb.,Umbilical vein. It shotdd also l)e noted that the absence of rotation of thechicks stomach (as contrasted with nuunmals) and the lesserdevelopment of the ^reat omentum ai)pear to be the causes ofthe more primitive position of the spleen in birds as contrastedwith nuimnials. CHAPTER XII THE LATER DEVELOPMENT OF THE VASCULAR SYSTEM
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