EMBRYOLOGY. 1 



Anatomy of a Human Embryo. 1 '— Dr. F. Mall has made a verv 

 complete study of the anatomy of an embryo of 7 mm. having ahout 

 27 somites and an age closely di termined u twenty-ox days. 



The embryo was cut into 351 transverse sections and every other 



one of these drawn upon wax plates 2 mm. thick. The wax actions 

 were kept in normal relative position in a plaster mould while the 

 various internal organs, wen- gradually directed out. 



In this way a complete model of the internal organs, as solid bodies 

 seen by removing the overlying tissues from one side of the body, was 

 obtained and subsequently reproduced in a colored lithograph. 



A most striking and instructive demonstration of the anatomy of the 

 embryo at this early period is thus represented in Plate 30. The brain 

 and medullary tube, spinal ganglia and auditory vesicle, digestive 

 tract with its branchial pouches, bronchi, pancreas, liver and cloaca 

 together with the Wolffian bodies and ducts, the venous and the 

 arterial parts of the heart and vascular trunks are all represented as 

 solid objects seen in perspective and in a distinguishing color for each 

 system. 



The body cavity wi m permanent metal casts 



made by first casting the hollowed out space in the wax model with 

 Wood's metal, then making a plaster cast of this and finally filling the 

 plaster cast with solder. In this way is shown the origin of the lesser 

 peritoneal cavity as a right diverticulum, near the stomach, communi- 

 cating with the main eoelom by a constriction that remains as the 

 foramen of Win slow. This becomes of considerable intere.-t from the 

 comparative stud v made l»y the author in a preceding number of the 

 same journal, for it is there shown that the single right diverticulum 

 of higher mammals is found in some lower ones and the chick, along 

 with a left diverticulum that early disappears. In some reptiles again 

 both right and left diverticula remain in the adult though even here 

 the right is larger. The ichthyopsida appear to have neither of those 

 diverticula. 



Thyreoglossal Tract and the Hyoid. 1 — From the study of 

 sections of a human embryo of 16 mm. Prof. His is led to bring his 



•This department is edited by Prof. E. A. Andrews John, Hopkins IniveH y. 



