Normal plates of the development of the rabbit (Lepus cuniculus L.). 23 
a ——————— 
Nose and Mouth | Table 
| No. 
ı 
Ear 
r 
Ductus endolymphaticus a little longer than at 11), days. Otocyst considerably | Nasal pits deeper than at 12 days, more tubular. Anlage of JACOBSOoX’s organ | ES, 
elongated dorso-ventrally. 
Otocyst narrow from side to side in dorso-ventral section. Beginning of cochlea, 
as long narrow ventral prolongation of otocyst. Ridge of external semicircular 
canal anlage. 
Ridges of posterior and anterior semicircular canals. 
Long narrow ductus endolymphaticus with saccus endolymphaticus indicated. 
Well marked anlagen of external, posterior and anterior semicircular canals, 
the latter partly formed. Well marked anlage of cochlea (scala media) extending 
cephalad, slightlyconcave dorsally. Beginning differentiation of utricle and saccule. 
Small saccus endolymphaticus. Posterior, external and anterior semicircular 
canals completely formed and tubular. Saccule well marked. Anterior (or 
ventral) end of cochlea has just begun to turn. Anlage of periotic capsule of 
slightly condensed mesenchyma. 
Saccus endolymphaticus well marked. Narrow ductus endolymphaticus opens 
into narrow region between utricle and saccule, which are now well formed. 
Anterior (or ventral) end of cochlea (scala media) turns outward and caudad. 
Anlage of periotic capsule of condensed mesenchyma. 
Saccus endolymphaticus quite large. Anterior and external semicircular canals 
small in cross section. Utricle and saccule well marked. Anterior end of 
cochlea turned over for some distance. Periotic capsule precartilaginous. 
Anterior end of cochlea (scala media) makes one complete turn. Anlage 
of macula acoustica of utricle.e. An ampulla at both anterior and posterior 
openings of external semicircular canal into utricle. Narrow canal between 
saccule and cochlea, canalis reuniens. Periotic capsule precartilaginous. 
Anterior end of cochlea makes more than one complete turn. Ganglion spirale 
clearly formed. Anlage of macula acoustica of utricle well marked. Ampulla 
of common opening into utricle of anterior and posterior semicircular canals. 
Opening of ductus endolymphaticus into narrow canal between utricle and 
saccule is very close to canalis reuniens between saccule and cochlea. Periotic 
capsule nearly cartilaginous. 
Cochlea now makes one complete turn and about °/, of a second. Suggestion 
of macula acoustica of saccule. Periotic capsule cartilaginous. 
very small, merely a concavity on inner wall of nasal pit. Anteriorly, nasal 
pits wide open, posteriorly closed by an epithelial membrane. | 
Nasal pits deeper than at 12!/, days, more extended; their openings narrower. 
Anlage of JacoBson’s organ deeper. | 
Anlage of JACoBSoN’s organ more tubular. Posterior portion of nasal cavity 
bounded toward mouth cavity by solid epithelial bar. 
Anterior nares of noticeably smaller extent than in I3 day embryos. A little, 
| caudad of anterior nares, nasal cavities are entirely enclosed in mesoderm. 
| Posterior portions of nasal cavities in part open to mouth cavity, in part closed 
bya delicate epithelial membrane. JACOBSoN’s organ a blind tube of some extent. | 
| 
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| 
| 
| 
Anterior nares small: a little caudad of them, nasal cavites completely enclosed| 
in mesoderm. Posteriorly, nasal cavities open to mouth cavity, forming primi- | 
tive choanae. Mouth cavity narrow. Anlage of submaxillary gland? short 
evagination of oral epithelium, nearly solid. Short solid anlage of parotid 
gland at side of mouth. | 
External nares small, closed by solid epithelial plug. Maxillary processes extend | 
well forward. Nasal cavities open to mouth cavity. Tongue projects up be-, 
tween small palate shelves. Narrow mouth cavity. Solid anlage of submaxillary 
gland, with small buds, surrounded by condensed mesenchyma. Small solid 
anlage of parotid gland surrounded by a little condensed mesenchyma. Ducts| 
of both glands solid. | 
Narrow external nares closed by solid epithelial plug. Palate shelf a little more 
prominent than at 16 days; tongue projects above it. Anlage of submaxillary | 
gland lobulated, quite solid; its duct solid. Anlage of parotid gland slightly 
lobulated, quite solid. Two median enamel organs with dental papillae in both 
upper and lower jaw. These structures are disconnected from the dental 
ridges? more posterior. Turbinal fold? 
External nares plugged by epithelium. Two distinct median enamel organs 
and dental papillae in both upper and lower jaw, germs of median incisors? 
Two turbinal folds? Submaxillary gland larger than at 16!J, days, more lobulated, 
quite solid. Parotid gland similar. Dental ridges? in upper and lower jaw., 
Palate shelf larger. | 
| 
| 
External nares plugged with epithelium. Two median tooth germs in upper! 
and lower jaw show beginning dentine formation. Palate shelves meet each other 
| below nasal septum. Enamel organ and dental papilla of tooth germ in both 
upper and lower jaw, apart from those in median line in front. 
External nares plugged with epithelium. Palate shelves fused with nasal septum | 
separating nasal from mouth cavity. Submaxillary gland larger than before, 
more branching buds, some of which show a minute lumen. WHARTON’S duct in, 
part solid. Parotid gland quite extensive; a few tubules show a minute lumen. | 
STENSOoN’s duct shows in part a minute lumen, | 
