Normal plates of the development of the rabbit (Lepus cuniculus L.). 9 
below the auditory cleft. There is no visible trace of a cervical sinus or of third and fourth gill arches. 
The milk line is clear though small. Both fore and hind limb buds show a division into two parts; a con- 
dition which is, however, better marked in the fore limbs. The distal part is curved on the edge, broader, 
but flattened from side to side; it is, in the fore limb, the beginning of the manus; in the hind limb, the 
beginning of the pes. Myotomes are visible externally from a point just cephalad of the roots of the fore 
limbs to the tip of the tail. Compare, for internal development, Tables Nos. 16 and 17. 
The more important changes in this I3-day embryo as compared with that of 12'/, days are the 
following: the head is larger and projects more; the trunk is considerably straightened though not much 
more than at 12!/, days; the heart chamber is relatively less prominent, while the abdomen has become 
more prominent; the tubercles of the external ear are more distinct; the outlines of the mandibular and 
hyoid arches have, consequently, become obscured; these arches also now meet below the auditory cleft; 
there is no longer any trace of the cervical sinus; the milk line has appeared; the hind limb as well as 
the fore limb shows the division described above; both limbs are larger. This 13-day embryo was rather 
large in measure, though in degree of development it makes a very good stage between the 12!/,-day and 
14-day embryos. 
Fig. 30 (X 5). 
z The description is taken from a specimen closely similar to that figured and of the same age. 
Embryo of 14 days after coitus. Measured in longest diameter 10.6 mm.: vertex-brow, 5.6 mm.; vertex-neck, 
5.0 mm. ZENKER fixation. The head projects beyond the heart chamber so far that while the mouth over- 
lies the latter, the brow and anterior nares nearly touch the umbilicus and umbilical cord. A very small 
interval only separates the tail from the brow. The head bend is right-angled. The neck bend forms a 
close obtuse rather than a right angle. The trunk bends gradually to the region of the hind limbs where 
the caudal end of the body turns straight upward toward the head and remains nearly in the median line. 
The tip of the tail is bent away from the umbilicus. The outlines of the hemispheres are easily distinguish- 
able. The eye is prominent, the lens distinct, as also retinal pigment. There is a slight elevation in the 
region of the mid-brain. The thin expanded roof of the fourth ventricle is visible. The auditory cleft is 
closed below but has a wide opening. The pinna projects. The maxillary process is more prominent than 
the mandible on lateral view. There is no distinct hyoid arch. "The manus shows distinct traces of a 
beginning division into digits; the pes also, but perhaps a little less clearly marked. Both palms and soles 
face mesad. The milk line is in part divided into separate mammary anlagen. Myotomes are rather 
indistinct in the cephalic half of the trunk; in the caudal half, they are plainer. Compare, for internal 
development, Table No. 18. 
The more important changes in this 14-day embryo as compared with that of 13 days are the follow- 
ing: the overhanging head is nearer the umbilicus; the auditory cleft is completely closed below; the 
pinna now projects a little; the hyoid arch, as a distinct structure, has disappeared ; the thoracic region is 
less prominent, the abdomen more so; the limbs are clearly larger and show the beginning digital divisions; 
the milk line has become separated in part into the mammary anlagen. 
Fig. 31. (X 9). 
The description is taken from a specimen closely similar to that figured and of the same age. 
Embryo of ı5 days after coitus. Measured in longest diameter 12.4 mm.: vertex-brow, 5.6 mm.; vertex-neck, 
Normentafeln zur Entwicklungsgeschichte der Wirbelthiere V. 2 
