ars to 
‚ atrio- 
ı walls 
SrloSus 
y)eared. 
en 3rd 
nd 5th 
larger 
JUVIER 
eptum 
ricular 
stemic 
wever. 
aortic 
tween 
. Two 
large. 
ramen 
rentri- 
nearly 
(asin 
|onary 
gone. 
arch. 
1ected 
Large 
US)AL . 
rsally 
> arch 
of left 
aortic 
hence 
r any 
trunk 
ırches 
ıction 
' does 
Pul- 
t still 
now 
yilical 
’ non 
aorta 
uricle 
:fore; 
scles 
Normal plates of the development of the rabbit (Lepus cuniculus L.). 27 
Integument 
Extremities 
Amnion 
Allantois 
Ectoderm apparently two-layered. Beginning 
of milk line; a slight thickening and ridge of 
ectoderm. 
Ectoderm apparently two-layered. Separated (?) 
mammary gland anlagen; small ectodermal 
thickenings projecting from surface. 
In snout, hair anlagen; short inward projec- 
tions of ectoderm. Anlage of hair papilla 
underneath, a thickening of mesoderm. Ecto- 
derm probably two-layered? Separate mam- 
mary anlagen. 
Hair anlagen in snout about same as at I5 days. 
Mammary anlagen a little larger; do not project. 
Ectoderm perhaps two-layered ? 
In snout, hair anlagen larger than at 16 days. 
Hair papilla more distinct. Beginning of hair 
bulb. Mammary anlagen about same as at 
16 days. Ectoderm perhaps more than two- 
layered ? 
Mammary anlagen small, solid ectodermal 
growths into the mesenchyma. 
In snout, hair anlagen a little larger: hair 
bulbs and papillae a little more distinct than 
before. No projection from surface. 
In snout hair anlagen about same as at 18 days. 
Small hair anlagen on dorsum, sides and belly 
of body. Mammary anlagen solid; only a little 
larger than before. Ectoderm probably more 
than two-layered. 
| as fore. 
About the same condition as at ıI'/, days. 
Fore limb more advanced; in section a distal 
thinner and a proximal thicker portion. Limb 
bud still composed of condensed mesenchyma. 
Spinal nerve in limb. Hind limb about same 
A proximal thicker part of fore limb, a distal 
narrower part. Proximal part contains areas 
of pre-cartilage. Hind limbs essentially the) 
same. 
In fore limb, cartilaginous anlagen of humerus. 
radius and ulna; the two latter rather semi- 
cartilaginous. In hind limb, anlagen of femur, 
tibia and fibula, rather pre-cartilaginous. 
Scapula marked out in cartilage. Cartilaginous 
humerus, radius and ulna. Muscle anlagen 
about them. Cartilaginous os innominatum, 
ln tibia and fibula. Muscle anlagen about 
them. 
No important differences from 16-day embryo. 
Appendicular skeleton cartilaginous. 
Beginning ossification in shaft of humerus, 
and, very slightly, in shaft of femur. Sug- 
gestion of beginning ossification in shafts of 
radius and ulna. 
Ossification in scapula, in shafts of humerus, 
radius and ulna. Quite extensive ossification 
in shaft of femur. Slight ossification in os| 
innominatum and in shaft of tibia. Suggestion 
of beginning ossification in shaft of fıbula. 
Allantois a little expanded a little above, 15. 
entrance of Wolffian ducts into cloaca. | 
Urogenital sinus now becoming differentiated. 
Allantois stalk in ventral abdominal wall small.| 17. 
Urogenital sinus almost completely separated | 18. 
from rectum; only a solid epithelial connection. 
| Allantois stalk in ventral abdominal wall very 
small. 
Allantois at point of entrance into umbilical| 19. 
| cord very small. 
| 
| 
Beginning of bladder and urethra indicated. 20. 
Just below umbilicus, allantois very small. 
Expanded allantois (bladder) reaches to lower 21. 
level of umbilicus. Allantois at umbilicus, 
passing into umbilical cord, very narrow. 
Allantoic arteries and allantois, imbedded in 
mesenchyma, project strikingly into coelom 
from ventral abdominal wall. | 
Allantois entering umbilical cord extremely | 22. 
small. Bladder has more than one layer of 
epithelium. 
Narrow allantoic stalk, hollow, from bladder| 23. 
to umbilicus. Allantois entering umbilical cord 
very narrow. 
Like condition at I$ days. Bladder epithelium | 24. 
with underlying mesoderm much folded. | 
