1 66 MALL. [Vol. V. 



finally by disappearance of the septa, the whole body-cavity is 

 caused to communicate with the false amnion. 



In this abstract I have included only what directly interests 

 us, leaving the many interesting details regarding the develop- 

 ment of the lymphatics. 



The sprouting of the pleuro-peritoneal cavity *rofn the peri- 

 cardial places the omphalo-mesenteric veins on the ventral side 

 of the former and on the dorsal side of the latter. After the 

 intestinal canal is formed, it is placed on the dorsal side of 

 the pericardial, and between the pleuro-peritoneal cavities, the 

 septum separating the pleuro-peritoneal forming the mesentery, 

 — a condition which remains in the adult in fishes and amphibia. 



The first clear idea obtained regarding the development of 

 the lesser peritoneal cavity and great omentum was given by 

 Johannes Miiller in 1830. 1 To him we owe our knowledge of 

 the mesogastrium, and the confirmation of Meckel's descrip- 

 tion 2 of the relation of the omentum to the colon. 



The whole subject has been thoroughly re-worked by Toldt, 3 

 beginning with human embryos of about the sixth week, — the 

 same stage with which Miiller started. 



The present communication is intended to partly fill the gap 

 between the works of Budge and of Toldt. This was made pos- 

 sible by a modification of Selenka's method by which "corrosion 

 preparations" of very young embryos are obtained. 4 I proceed 

 as usual to reconstruct according to the method of Born, but 

 instead of blending the plate, the portions which are to appear 

 in the corrosions are cut out. If the portions cut out represent 

 spaces, the process is simple, as for instance, blood-vessels or 

 the ccelom. The plates are now piled, and the spaces filled with 

 Wood's metal or plaster of. Paris. The former is better, if the 

 spaces are small. After the plaster has set, the wax may be 

 removed by boiling in water ; while, if the injection has been 

 made with Wood's metal, the plates are simply to be pulled off. 

 For all ordinary small models, the metal is, by all odds, the 

 most desirable. The metal cast can now easily be polished 

 or smoothed over with wax, and the whole buried in plaster 



1 Miiller, Meckel's Archiv, Bd. V. 



2 Meckel, Meckel's Archiv, Bd. III. 



3 Toldt, Denkschriften d. Akademie zu Wien, Bd. 41, 1879. 



4 Selenka, Setzungsber. d. physiol. vied. Soc. zu. Erla7igen, 1886. 



