170 APPENDAGES OF THE FOETUS. 



444. This stem is unquestionably hollow until the twentieth or 

 thirtieth day, for I was able in two specimens to squeeze the liquid 

 from the vesicle into the intestine without rupturing any thing; 

 whence it follows that the objections of MM. Emmert, Hcech- 

 stetter, Cuvier, &;c. are of no value, at least in so far as they are 

 applicable to man. It becomes obliterated at a period wliich has 

 not appeared to me to be always the same; in general, however, it 

 may be said to be no longer permeable at five weeks, and its oc- 

 clusion takes place from the navel towards the vesicle in proportion 

 as the cord becomes more complete. 



445. The parietes of the vitelline sac are strong, resisting, pretty 

 thick, and difficult to lacerate; they have never appeared to me to 

 be more frail than the other membranes of the ovum, unless they 

 had been previously rendered thinner by some morbid change or by 

 some mechanical cause. Smooth and even when the vesicle is 

 full, they wrinkle or fold, on the contrary, when that little body is 

 emptied; they are generally of a yellowish color, but perhaps this 

 tint depends upon the fluids they contain; their transparency too is 

 imperfect, which may depend upon the same cause. 



446. Those who have examined the umbilical vesicle in brutes, 

 and who have admitted its continuity with the intestines, pretend 

 that it is composed of three laminse. According to M. Dutrochet 

 the same is observable in the human species, but, so far as I know, 

 this is only a mere assertion advanced without proof. However, as 

 to the vesicle, I have never in any instance found it to consist of 

 several membranes; its pedicle in particular is homogeneous and 

 not lamellated. So that I think we may very well admit in this 

 apparatus the existence of a mucous surface and a serous surface, 

 but not of a serous membrane and a mucous membrane; still less 

 of a muscular coat: besides, it is not until a much later period of 

 life that these distinctions of the tissues are effected, even in those 

 organs where they are subsequently most decided (166). 



447. However this may be, arterial and venous vessels are visibly 

 distributed upon it; I have observed them not only in the substance 

 of the parietes of the vitello-intestinal canal, but also in those of 

 the vesicle itself; in the latter twice, and more than twenty times in 

 the former. In the former case I saw them compose a very beautiful 

 net work with arborescent ramifications extremely easy to follow, 

 without any particular preparation, and even with the naked eye. 

 In the latter, they consisted of two trunks becoming larger and larger 

 as they approached towards the abdomen. 



448. These vessels, denominated the omphalo-mesenterlc vessels, 

 would be better named vitello-mesenteric, or simply vitelline. Ac- 

 cording to my own observation, they do not empty themselves into 



