side of the embryo, which Baer at first suggested as the 

 heart and liver, but he then indicated an error, against 

 which he warned other investigators. The anterior projec- 

 tion proved to be the lower jaw, which together with the 

 hypoglossal bone formed from the anterior pair of the 

 branchial arches, protruding more than the others. Behind 

 the projection of the lower jaw, two dark cavities appear. 

 Doubtless these are the branchial slits, which do not yet 

 penetrate the cavity of the pharynx. The posterior pro- 

 jection of the ventral side is the heart, to which a semi- 

 canal is affixed, representing the rudiment of the digestive 

 tract, separated during the preparation from the union with 

 the yolk duct; the passage of the abdominal layers into the 

 amnion is also torn. The embryo still has no trace of 

 extremities. The age of the embryo cannot be determined 

 with complete exactness. In any case, Baer assumed it 

 related to a somewhat later stage of development than did 

 the embryo described by Pokel's and was sixteen to twenty 

 days after conception. 



Cases 4 and 5 were described briefly due to the 

 unknown length of pregnancy, both approximately three weeks. 



Case 6, an embryo three to four weeks old, (Fig* 4 and 

 6) is described in more detail. The mouth of the embryo was 

 closed, and the branchial slits were not seen, neither from 

 outside nor from the cavity of the pharynx, which was con- 

 sidered an abnormally slow development at this age. The 

 wide stomach, without limits, entered the intestine, while 

 there was an impression that the stalk of the umbilical 

 vesicle was united with the stomach. In the embryo the cord 

 and brain were clearly seen; the ventricle of the heart 

 remained single, but in it the dividing fold had begun to 

 form. In the described case, for the first time in the human 

 embryo, both roots of the aorta could be seen. The lungs 

 were clearly divided into lobes. In the posterior part of 

 the abdominal cavity the urinary bladder was present, extend- 

 ing into the stalk of the allantoic sac. Beside the vertebrae, 

 the posterior halves of primary kidneys were seen. 



Case 7, an embryo of five weeks, was very superficially 

 investigated in 1822, because it was obtained in very damaged 

 condition. 



445 



