. The development of the chick; an introduction to embryology . pneumato-entericus sinister. 1. Br.,Left bronchus. Prv., Proventriculus. Rhesin., Recessus hepato-entericus sinister. Rpesin., Right pneumato-enteric recess. Otherabbreviations as in Fig. 195. According to Choronschitzky, the peritoneal cells invade theneighboring mesenchyme, and, spreading through it, form an ill-defined denser area, the fundamental tissue of which is thereforemesenchymal. The meshes of the latter are in immediate con-tinuity with the vena lienalis, but the vascular endothelium is THE BODY-CAVITIES 347 not contin
. The development of the chick; an introduction to embryology . pneumato-entericus sinister. 1. Br.,Left bronchus. Prv., Proventriculus. Rhesin., Recessus hepato-entericus sinister. Rpesin., Right pneumato-enteric recess. Otherabbreviations as in Fig. 195. According to Choronschitzky, the peritoneal cells invade theneighboring mesenchyme, and, spreading through it, form an ill-defined denser area, the fundamental tissue of which is thereforemesenchymal. The meshes of the latter are in immediate con-tinuity with the vena lienalis, but the vascular endothelium is THE BODY-CAVITIES 347 not continued into these meshes. Thus free embryonic cellsof 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 ofpropinquity. Gon. 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
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