No. 2.]| DEVELOPMENT OF THE HUMAN COELOM. 421 
that the specimen was excellently preserved. In the greater 
portion of the neural tube the tissue is already marked by two 
zones, a central one rich in nuclei, and a peripheral containing 
none. This corresponds with the description already made 
familiar to us by His. 
The general shape of the whole central nervous system is 
very unlike that of any other young human embryo ever pub- 
lished. It circumscribes the greater portion of a circle, while 
in the other human embryos of this size it makes more of a 
straight line. I think that it is probable that this specimen 
represents the normal, as it was not injured nor handled in 
any way before it was cut into sections. 
The entoderm, as the figures show, is already divided into 
fore-gut, mid-gut, and hind-gut. The fore-gut makes the 
pharynx, from which there are four diverticula on the dorsal 
side, one on the ventral side, and two near the mouth. The 
four on the dorsal side mark the first two branchial pockets on 
either side of the embryo ; the two in front are Seessel’s pocket 
and the entodermal portion of the mouth ; while the one on 
the ventral side of the pharynx is the beginning of the median 
portion of the thyroid gland (Fig. 17, t.). 
At the junction of the pharynx with the umbilical vesicle 
there is a large diverticulum into the septum transversum, Fig. 
18 1, the beginning of the liver. 
Within the tail end of the embryo, behind the neurenteric 
canal, the hind-gut is enlarged considerably, and from it the 
entodermal canal of the allantois arises. 
The whole umbilical vesicle is covered with blood-vessels 
which communicate with the veins and arteries of the embryo. 
Near the origin of the liver there are two veins which collect 
the blood from the umbilical vesicle and then enter the heart. 
These are the omphalomesenteric veins. They with a num- 
ber of their branches are shown in sections in Fig. 18, v. 
The heart itself is broken, but there is enough of it left to 
show that it is bent upon itself and contains a large cavity at the 
point where the veins entered it. From the heart two arteries 
arise and pass in front of the first branchial pocket, and each 
follows the course as shown in black in the reconstruction. 
