358 OF CONCEPTION. 



but for a very short distance, and, indeed, soon disap- 

 pears altogether. In other mammalia it leads to the 

 allantoid,* which is universally acknowledged to be 

 absent in the human feetus. For I think that the pro- 

 blematical vesicula umbilicalis, found in human ova be- 

 tween the chorion and amnion, f is not analogous to the 

 allantoid % but to the tunica erythroides that is seen in 

 the ova of some mammalia, and to the vitellary sac of 

 the incubated egg. It is found in healthy human ova, 

 the second or third month after conception, too fre- 

 quently and of too constant an appearance to be re- 

 garded as accidental, morbid, or monstrous.§ 



* Vide Fabr. ab Aquapcndente, De Formato Foetu. tab. xii. xiii. xiv. xvii. 

 fig. 27. xxv. 



T Vide Continental. Soc. Reg. Sc. Gottingens. vol. ix. p. 128. fig. I. 



X Among tbe moderns who have compared it to this, are J. F. Lobstein, 1. c. 

 fiber die Ernahrung des Foetus ; and C. H. D'Zondi, Supplem. ad Anat. 

 et Physiol. 



§ The opinions both respecting the natural constancy of the vesicula umbi- 

 licalis and its analogy to the tunica erythroides, I originally, as far as I know, 

 proposed upwards of twenty years since, in the first edition of these Institu- 

 tions (1787), and in my Specimen Physiologic Comparatte (1788) formerly 

 quoted. 



The connection of this vesicle with the intestinal canal of the embryo, and 

 indeed with the appendix vermiformis of the caecum, is shewn by Laur. Oken in 

 his and Diet. G. Kiesor's Beytr. zur Vergleichenden Zoologie, &c. Fasc. i. ik 

 Bamberg. 1806 sq. 



See' likewise Kieser's Ursprung des Darmkanals aiis dcr vesicula umbilicalis , 

 dargestellt im menschlichen Embryo. Goett. 1810. 4to. 



But, on the contrary, Fr. Meckel shews it to be united with the diverticulum 

 of the small intestines (Diverticulum Littrianum), Beytr. zur vergleichenden 

 Anatomic. Vol. i. Fasc. i. Lips. 1808. p. 93 ; and more fully in Reil and 

 Autenreith's Archiv.fur die Physiologie. Vol. ix. p. 421. 



Consult, among others, W. Hnnter, Anatomical Description of the Human 

 Gravid Uterus (a posthumous work edited by Matthew Baillie). Lond. 1794 

 ■Ito. p. 40 sq. 



B.N. G. Schreger's letter to Sommcrring, De functione placenta uterintr. 

 Erhmp. \7'J0. 8vo. 



