346 THE DEVELOPMENT OF THE CHICK 



to the left side of the body-cavity (Fig. 188), and which is 

 exaggerated by the rapid growth of the dorsal pancreas (Choron- 

 schitzky). The spleen is thus genetically related to the wall of 

 the great omentum, and lies outside the cavity of the latter. 

 The cells of the spleen are proliferated from a peritoneal thicken- 

 ing, which may be compared in this respect to the germinal 

 epithelium. It is recognizable at ninety-six hours, and the mass 

 formed by its proliferation grows rapidly, forming a very consid- 

 erable projection into the left side of the body-cavity above 

 the stomach, at six days (cf. Fig. 197). 



IBr , 



-Of. 



Bo ma/ 



FIG. 196. The same model from the left side. (After Broman.) 

 Hrpesin., Hiatus recessus pneumato-entericus sinister. 1. Br., 

 Left bronchus. Pr'v., Proventriculus. Rhesin., Recessus hepato- 

 entericus sinister. Rpesin., Right pneumato-enteric recess. Other 

 abbreviations as in Fig. 195. 



According to Choronschitzky, the peritoneal cells invade the 

 neighboring mesenchyme, and, spreading through it, form an ill- 

 defined denser area, the fundamental tissue of which is therefore 

 mesenchymal. The meshes of the latter are in immediate con- 

 tinuity with the vena lienalis, but the vascular endothelium is 



