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lorsal 
Normal plates of the development of the rabbit (Lepus cuniculus L.). 25 
Digestive Tract. Liver. Pancreas. Spleen 
Respiratory Tract 
Lesser peritoneal cavity formed; foramen of WINSLOW narrow. Numerous solid liver trabe- 
culae. Division of liver into lobes indicated. Anlage of gall bladder has a minute cavity. 
Dorsal pancreas mostly a solid cell mass branching irregularly. Ventral pancreas small, 
solid. Gut loops into umbilical coelom. Very early anlage of coecum? Cloaca small. Anal 
membrane intact. Post-anal gut distinct with lumen. 
Some condensed mesenchyma about epithelium of oesophagus. Liver larger, trabeculae | 
more closely arranged than at ı2'/, days. Gall bladder dpparently quite solid. Stomach 
larger than before. Dorsal pancreas composed of bands of cells some showing a lumen. 
Ventral pancreas shows a small lumen. Blind end of ventral pancreas apparently uncon- 
nected with dorsal pancreas. Gut loops into umbilical coelom. Cloaca. Anal membrane 
intact. Post-anal gut has in part disappeared. 
Early anlage of spleen (?) as slight cell thickening in dorsal mesogastrium. No projection. 
| 
Stomach much larger than before; cavity expanded. Liver very large; trabeculae numerous, 
apparently solid, closely arranged. Foramen of WINSLOW narrow. Gall bladder solid. More 
than one connection of hepatic cords with ductus choledochus. Ventral pancreas clearly 
joins ductus choledochus. Ventral pancreas, partly showing a lumen, is connected with 
tubules of dorsal pancreas. The latter are numerous some showing a lumen. Gut extends 
well into umbilical coelom. Coecum is long. Rectum partly separated from uro-genital| 
sinus by mesenchyma. Anal membrane closed. No post-anal gut discernible. Early anlage 
of spleen. | 
Mesenchyma about oesophagus shows beginning differentiation into mucous and muscular 
coats. Liver very large; trabeculae closely approximated, apparently solid. Gall bladder 
solid. Cystic duct has a lumen. Several connections between liver substance and bile duct. 
Ventral pancreas has lumen, joins ductus choledochus. Many tubules of dorsal pancreas 
show a distinet lumen. Gut loops in umbilical coelom. Rectum completely separated from 
urogenital sinus. Anal membrane broken through apparently in a narrow line. Small anlage 
of spleen, projects slightly from dorsal mesogastrium. 
Oesophagus has a thick stratified epithelium, a small lumen ; beginning differentiation of 
mucous and muscular coats clearly indicated. Liver enormous. Gall bladder solid. Cystic 
duct with distinct lumen. Ductus choledochus with distinct lumen. Large pocket of stomach 
dorsal to entrance of oesophagus. Numerous tubules of pancreas, many showing a small 
lumen. Ventral pancreas, connected with ductus choledochus, joins tubules of dorsal 
pancreas. Beginning differentiation of mucous and muscular coats of small intestine. Rectum 
in part quite solid completely separated from uro-genital sinus. Anal membrane broken 
through; anus open. Spleen projects from mesogastrium. 
Oesophagus in part quite solid; its mucous and muscular coats more distinct than before. 
No important changes in this embryo as compared with that of 16 days. Spleen makes a 
small projection from dorsal mesogastrium. 
Differentiation of muscular coat of oesophagus into circular and longitudinal layers apparently 
beginning. Differentiation of mucous and muscular coats of stomach indicated. Epithelium 
of gall bladder vacuolated. Several hepatic ducts open into ductus choledochus; the latter 
of Considerable size. Numerous pancreatic tubules, mostly showing a lumen. ‘Islands of 
LANGERHANS indicated? Mucous and muscular coats of duodenum distinctly indicated; the 
muscular coat showing division into circular and longitudinal layers. Many coils of gut in 
umbilical coelom. Rectum in part quite solid. Anus wide open. 
| 
Ventral pancreatic duct, a small structure, opens into ductus choledochus and communicates 
with tubules of pancreas. Embryo not essentially different from that of 17 days. | 
Anlage of pharyngeal constrictor muscles. Mucous and muscular coats of oesophagus 
distinet; muscular coat is divided into circular and longitudinal layers. Mucous and muscular | 
coats of stomach distinct. Ventral pancreas joins ductus choledochus and pancreatic tubules. | 
Islands of LANGERHANS distinctly indicated? Mucous and muscular coats of rectum indicated. 
Cephalic portion of rectum has a cavity. Numerous intestinal coils, now entirely within 
abdominal coelom. Spleen, with narrow base, projects free from dorsal mesogastrium. 
Spleen long and slender. | 
Normentafeln zur Entwicklungsgeschichte der Wirbelthiere. V. 
Trachea for the most part separated from oesophagus by mesenchyma. 
Branch from left primary bronchus. Trachea appears continued| 
into right primary bronchus. | 
Anlage of larynx ? Trachea mostly separated from oesophagus by 
mesenchyma. Epithelium of trachea quite thick; some condensed 
mesenchyma about it. Anlagen of lungs larger than before; right 
and left primary bronchi branched. | 
Anlage of larynx (?). Condensed mesenchyma about it and about 
trachea. More branching from primary bronchi than at 13 days. 
Considerable mesenchyma in lungs. Indication of division of right 
lung into lobes. Right lung larger than left. Pleural cavities open 
to abdominal coelom. | 
Anlage of larynx more distinct: much condensed mesenchyma about, 
it. Trachea begins at lower part of larynx; at this point trachea| 
is solid. Trachea quite large, with large lumen; condensed mes-| 
enchyma about it. Tubules in lungs more numerous than before. | 
Considerable mesenchyma in lungs. Right lung has a small ventral 
lobe. Left lung lobed. Pleural cavities completely closed cephalad; 
open to abdominal coelom. | 
Much condensed mesenchyma about anlage of larynx. Trachea has 
stratified epithelium; about it condensed mesenchyma, especially 
ventrally. Lungs larger than before; both are lobed. Right lung, 
has a ventral lobe. Much mesenchyma in lungs. Right and left 
pleural cavities open into abdominal coelom by minute passages. 
Anlage oflarynx has a cavity ventrally and not elsewhere. Anlagen 
of tracheal cartilages of condensed mesenchyma. Eparterial bronchus | 
in right lung. | 
| 
| 
Epiglottis quite large, mesenchymatous. Some laryngeal museles | 
indicated. Thyroid cartilage; cricoid cartilage. Eparterial bronchus 
inright lung. Much mesenchyma in lungs. Pleural cavities extend 
well ventrad; they are completely closed caudad. 
Anlage of small amount of smooth muscle in dorsal wall of trachea. | 
| Muscle coat about larger bronchi indicated. 
Epiglottis quite long, mesenchymatous. Larynx nearly solid. Some | 
laryngeal muscles distinct. Thyroid and cricoid cartilages distinct. 
Cartilaginous tracheal rings. Trachea has stratified epithelium. 
Trachea has no glands. Pre-cartilage about primary bronchi.| 
Considerable mesenchyma- in lungs but less proportionally than 
before. Ventral lobe of right lung. | 
