Se N We er un 
Io Normentafeln zur Entwicklungsgeschichte der Wirbelthiere, 
4.4 mm. ZENKER fixation. The head projects far forward but the nares and brow are separated from the 
umbilical cord by a considerable interval. The mouth faces downward toward the pericardial wall, from 
which it is not far distant. The head bend is nearly right-angled. The neck bend forms an obtuse angle. 
The hind limbs are directed ventrad rather than upward toward the head; they are nearly in a direct line 
with the fore limbs. The caudal end of the body is bent up between the hind limbs. The tip of the tail is 
bent away from the body. The abdomen is as prominent as the thorax. The anterior nares are small; the 
mouth wide. The eye with the lens is prominent. The lid folds appear, though small. There are hair 
anlagen visible on the maxilla and one large hair anlage under the eye. The pinna projects over the 
external auditory opening. There are on manus and pes ridges, with shallow grooves between, indicating 
the formation of digits. The palms face mesad and a little caudad; the soles face mesad. There are 
separate mammary anlagen. Myotomes are indistinct cephalad of the roots of the hind limbs. Compare, 
for internal development, Table No. 19. 
The more important changes in this 15-day embryo as compared with that of 14 days are the follow- 
ing: the head is now at a noticeably greater distance from the umbilicus; the neck bend has begun to 
straighten; the trunk has straightened so much that the hind limbs are directed ventrad more than upward 
toward the head; the abdomen has become as prominent as the thorax, which no longer projects in such 
a striking manner as in the younger stages; the lips have begun; hair anlagen appear on the maxilla and 
one under the eye; the pinna projects more over the external auditory opening; digital divisions on manus 
and pes are more distinct. 
Fig. 32 (X 5). 
The description is taken from a specimen closely similar to that figured and of the same age. 
Embryo of 16 days after coitus. Measured in longest diameter 16,2 mm.; brow-snout, 4.4 mm.; vertex-brow, 
6.6 mm.; vertex-neck, 4.6 mm. ZENKER fixation. The top of the head forms nearly a right angle at the 
brow with the line of the face. The head bend at the vertex is essentially right-angled. The neck bend makes 
a wide obtuse angle. The head is somewhat elevated. There is a striking prominence at the vertex in the 
region of the mid-brain. The back is straight nearly to the level of the hind limbs where the body curves 
gradually around until the short tail projects ventrad in the median line between these extremities, which 
extend a little farther than the tip of the tail. The abdomen is more prominent than the thorax. The 
mouth and nares face downward (caudad). The snout projects a little. There are numerous hair anlagen 
on the maxilla; four distinct above the eye; one below. The mandible is not prominent. The lid folds 
are small. The pinna projects over the external auditory opening. The manus and pes show distinct digital 
divisions; the manus, five in all; four larger, one on the median, originally upper, side smaller: the pes, four 
in all. In both manus and pes these divisions are connected. The palms look downward; the soles mesad. 
There are three distinct mammary anlagen visible on lateral view. Myotomes are distinguishable only in 
the tail. There are coils of intestine in the umbilical cord. Compare, for internal development, Table No. 20. 
The more important changes in this 16-day embryo as compared with that of ı5 days are the follow- 
ing: the snout is more distinct and more prominent; the neck bend is much reduced, and, as a consequence, 
the head is more elevated; a striking prominence in the region of the mid-brain has appeared; the trunk 
is still more straightened; the hind limbs project ventrad, and the tail also; the abdomen is more prominent 
than the thorax; the pinna projects more; the fore limb has turned so that the palm faces downward or 
caudad; myotomes can only be made out in the tail. 
