474 Description of a 4-mm. Human Embryo 
between the cords, and the thin endothelium becoming wrapped around 
the cords; and thus the adult condition will be reached. 
In this model is also shown the anlage of the pancreas. (Fig. 14, Pa.) 
It is a small, knob-like mass of cells, with no cavity, growing from the 
ventral border of the intestine just caudal to the liver outgrowth, but 
distinct from the latter. Further down the intestine (nine sections in 
the specimen) where it has begun to expand to the yolk sac, is found an- 
other, smaller mass of cells, growing also from the ventral border, which 
probably represents a second anlage of the pancreas; there is no sign of 
a dorsal anlage. The pancreas also, then, differs from those usually de- 
scribed, as it has probably two outgrowths, neither from the liver stalk, 
for the duct of Wirsung, and as yet no outgrowth to represent the duct 
of Santorini. There is no enlargement of the intestine above the liver 
for the stomach. 
MODEL OF THE TAIL END OF THE EMBRYO. 
This model has been photographed in two positions, once (Fig. 15) 
squarely from the right side, and again (Fig. 16) still from the right 
side, but also a little from behind. The left side of the model shows 
the surface of the embryo with the umbilical cord attached to it. <A 
portion of the right side, that at the tip of the rump, shows the outer 
surface also; but for the remainder of this side, the ectoderm of the skin’ 
and the mesenchyma have been dissected away to the median line, which 
in this part of the embryo is distinctly curved on account of the spiral 
twist of the tail. The curve can be clearly understood by referring to 
the photograph of a section (Fig. 8) at the level of the two brass handles 
for moving the model, shown in Fig. 16. The plane of section is shown 
by the bottom line of the dissected part of the model. The outline of 
this section will explain the irregularities of the surface at the rump end 
as seen in the model. Posteriorly, from the median line forward extends 
a rounded, smooth area overlying the spinal cord; next this anteriorly, 
another rounded area, broken by transverse grooves into irregular 
mounds, representing the primitive segments; and still more anteriorly 
a broad, smooth area, separated from the last by a longitudinal groove, 
covering the body wall, within which les the ccelom. ‘These three areas 
are curved upon themselves at the rump end, the protuberant body wall 
making a distinct ledge-like projection, as seen in the photographs (Figs. 
15, 16,28. ws): 
Spinal cord.—The spinal cord is shown in both drawings, appearing 
at the dorsal side of the embryo, directly under the ectoderm of the skin. 
