No. 3.] A HUMAN EMBRYO TWENTY-SIX DAYS OLD. 475 



The cavity next encircles the omphalo-mesentric vessels of the 

 cord extending to the outside of the body. Behind the cord 

 there is again a large communication from one side to the other. 

 On the ventral side of the intestines, from the junction of the 



P.P. 



. D. 



Fig. 2. — Corrosion preparation of gastric diverticulum of a human embryo 7 milli- 

 metres long. Enlarged 44 times. P. P., pleuro-peritoneal cavity; F. W-, foramen 

 of Winslow; G. D., gastric diverticulum. 



cord with the mesentery, a large papilliform projection hangs 

 into this cavity (P). Still farther back the cavity encircles the 

 Wolffian bodies, and finally ends by projecting deep into the tis- 

 sues of the pelvis. 



Alimentary Canal. 



A lateral view of the cast of the branchial region is shown on 

 PI. XXX. The entoderm is directly continuous with the ecto- 

 derm, and the cast is carried to the full exterior of the body. 

 On the dorsal median line the pocket which forms the hypophy- 

 sis, extending between the mid-brain and after-brain, is shown. 

 The first branchial pocket is bulbous and projects laterally, and 

 then passes as a marked groove on the ventral side of the bran- 

 chial cavity obliquely away from the mouth and towards the 

 median line. It is destined to form the Eustachian tube. 1 The 

 second pocket is equally as well marked but is hook-shaped, 

 with the point reaching half-way to the median line. The third 

 pocket points with its free extremity toward the second, and is 

 yet in free communication with the branchial cavity. It is des- 

 tined to become the thymus. The fourth pocket is irregular in 



1 Studies from the Biol. Lab., Johns Hopkins University, Baltimore, 1888. 



