Normentafeln zur Entwicklungsgeschichte der Wirbelthiere. 
As compared with the g!/,-day stage, this Io-day embryo shows the following more important 
changes: the head bend forms an acute angle rather than a right; the body is so bent as to leave the 
surface of the embryo, corresponding in position to the original dorsal aspect, of relatively small extent; the 
otic vesicles are no longer open to the exterior; the head and body cephalad of the anterior bend of the 
trunk, including the heart region have clearly grown larger; a gill arch posterior to the hyoid has appeared, 
as well as the first two clefts; the roof of the hind-brain has become kite-shaped. 
Ö Fig. 12 (X 10), 24 (X 5), and 24a (X 5). 
Embryo removed from uterus Io!l, days after coitus. ZENKER fixation. Measured 4.8 mm. longest 
diameter. Vertex-brow, 2.2 mm. Vertex-neck, approximately 2.8 mm. The head bend is nearly right- 
angled. The neck bend has appeared. In the region of the fore-limb bud, the body is bent approximately 
to the extent of a right angle. The caudal end of the embryo is bent over to the right so far as to make 
nearly one complete turn. The optic vesicle is evident. The thin ependymal roof of the hind-brain is 
conspicuous: its kite shape is very distinct. Alongside of the hind-brain the trigeminal ganglion is visible. 
The maxillary process, mandibular and hyoid arches are prominent. The cervical sinus is indicated. In it, 
the third and fourth gill arches are distinguishable but not very conspicuous. The first and second external 
gill clefts are very clear, the third much less so. The oral cavity is wide open. The mandibular arches 
barely meet in the mid-ventral line, in part do not. The auricular region, the ventricular limb and truncus 
arteriosus of the heart are easily visible through the thin pericardial wall. The fore limb buds form slight 
projections in the region of the main bend of the trunk. The hind limb buds also form slight projections 
on the upper part of the turn of the caudal end of the body but appear a little less prominent than the 
fore limb buds. Segments are visible externally to the number of approximately thirty-three. Compare, for 
internal development, Table No. ıı. 
The more important changes in this 10!/,-day embryo as compared with that of ıo days are the 
following: the neck bend has appeared but has progressed so far as to form an obtuse angle only with the 
line of the back; the caudal end of the embryo is rolled over to the right so far as to make nearly one 
complete turn; the ependymal roof of the hind-brain is more conspicuous; the cervical sinus is now indi- 
cated; the fourth gill arch and third external gill cleft have appeared; the fore and hind limb buds now 
make slight projections. 
5) Fig. 25 (X 5). 
Embryo removed from uterus II days after coitus. ZENKER fixation. Measured 5.4 mm. longest 
diameter: vertex-brow, 2.6 mm.; vertex-neck nearly 3.0 mm. The brow projects beyond the pericardial 
cavity and is separated from the caudal end of the body by.only a short interval. The head bend is 
nearly right-angled. The neck bend forms an obtuse angle with the line of the back. The main bend of 
the trunk approximates a right angle. The tail end of the body is bent over to the right. Shallow nasal 
pits are visible. The openings of the lentic vesicles are very distinct. The thin kite-shaped roof of the 
hind-brain is conspicuous; under it, the trigeminal ganglion. The maxillary process, mandibular and hyoid 
arches are prominent. The cervical sinus is well marked; in it appear the third and fourth gill arches. 
The first and second external gill clefts are very clear; the third less so, but evident. The mandibular 
arches touch the pericardial wall. The auricular region, the ventricular limb and truncus arteriosus of the 
heart are distinctly visible through the thin pericardial wall. The fore and hind limb buds project; the 
former a little more than the latter. Externally there are visible approximately 36 segments (or myotomes). 
Compare, for internal development, Table No. 12. 
