Normentafeln zur Entwicklungsgeschichte der Wirbelthiere. 
Hypophysis and Infundibulum 
Pharynx. Thyroid. Thymus 
| 18 
, days 
Infundibular evagination distinct; joined to top of hypophysis, which 
is slightly concave toward forebrain, a little expanded laterally, with 
narrow cavity. Hypophysis open to mouth. 
Infundibulum distinct but short; joined to top of hypophysis, which 
is quite long, open to mouth. 
Upper end of hypophysis expanded laterally; cavity narrow. 
Infundibulum a little longer than at 13 days, joined to upper end 
of hypophysis, which extends upward a little on either side of in- 
fundibulum. Upper end of hypophysis considerably expanded 
laterally. Hypophysis now not open to mouth but connected with 
oral ectoderm by a solid epithelial band. 
Infundibulum a little longer than at 14 days, overlies hypophysis 
more. Hypophysis bent concave toward fore-brain. Solid connecting 
band of epithelium between hypophysis and oral ectoderm. 
Infundibulum and hypophysis in essentially the same relation as at 
15 days. Cavity of hypophysis narrow. Beginning of cords of 
hypophysis, solid outgrowths from latter. Connection between 
hypophysis and oral ectoderm still traceable. 
Infundibulum open to brain; overlies hypophysis, which is bent 
toward fore-brain at an angle. Thick solid cords of hypophysis, 
very slightly vascularised. Connection between hypophysis and 
oral ectoderm still traceable. 
| Cords of hypophysis larger than at 16'/, days, more vascular. Still 
a slender connection between hypophysis and oral ectoderm. 
| Connecting band between hypophysis and oral ectoderm broken 
through just above latter; otherwise intact. Pituitary fossa well 
defined. 
Still a small connecting band between hypophysis and oral ectoderm. 
Infundibulum open to 3rd ventricle. Hypophysis much bent, contains 
a cavity. Two lateral upward prolongations of hypophysis on 
either side of infundibulum. Cords of hypophysis appear as a 
vascularised outgrowth of anterior wall of hypophysis, irregular 
in shape, solid except for contained vessels. Pituitary fossa well 
marked. 
Closing membranes of first, second and third gill pouches. Fourth gill pouch does 
not touch external ectoderm. Small solid medıan thyroid anlage joined to pharynx 
by a narrow stalk. Thymus anlage, small narrow tubular prolongations ventrad 
from 3rd pouch, open to latter. Lateral thyroid anlagen, tubular, small, open to 4th pouch. 
Ist gill pouch extends somewhat dorsad; its entoderm joined to ectoderm by short, 
solid epithelial rod. 2nd gill pouch not distincet. 3rd gill pouch very small: it has 
a solid epithelial connection with thymus anlage; the latter has a small cavity in 
part. The two thymus anlagen not connected. 4th gill pouch very small; a solid 
connection with anlage of lateral thyroid, probably unbroken? Lateral thyroid has a 
small cavity; does not reach median thyroid. Median thyroid has no connection with 
pharynx. 
Small tuberculum impar? 
Ist gill pouch narrow; no connection between entoderm and ectoderm. 2nd gill 
pouch not a distinct structure. 3rd gill pouch not distinct. Thymus anlagen have 
small cavities; have no connection with entoderm of pharynx; they extend farther 
caudad than median thyroid, to a point just cephalad of pericardial chamber; they do 
not meet each other. 4th gill pouch not distinct, a suggestion of primary epithelial 
connection with lateral thyroid. Lateral thyroid has in part a cavity; it meets the 
median thyroid, prolonged. The latter branched. 
Ist gill pouch narrow; has no connection with ectoderm; mesoderm intervening. 
2nd gill pouch not apparent. 3rd gill pouch not apparent. Thymus anlagen vascu- 
larised, show no cavity; they are not joined together; show no connection with 
pharynx. 4th gill pouch not apparent. No connection between lateral thyroid and 
pharynx apparent. Lateral thyroids have a minute cavity; they touch the dorso-cephalad 
prolongations of median thyroid; the latter solid. Anlage of tongue. 
Beginning differentiation of tongue muscle. Beginning of tympanic cavity; some 
expansion of peripheral end of ıst gill pouch. Thymus anlagen, solid, irregular bands 
of cells, somewhat vascularised; approach each other closely in median line but do 
not join; their caudal ends lie just cephalad of pericardial chamber; thymus anlagen 
extend cephalad to level of larynx. Median thyroid an extended mass of bands of 
cells, irregular in arrangement some showing a lumen; mesenchyma between them. 
Lateral thyroids show minute lumen; they touch wings of median thyroid. 
A little expansion in region of tympanic cavity; mesoderm separates ectoderm of 
external auditory canal from entoderm of tympanum. The caudal ends of thymus 
anlagen, just cephalad of pericardial chamber are separated only by a little mesen- 
chyma. Thymus consists of solid bands of cells, irregulary arranged. Median thyroid 
consists of numerous, irregular bands of cells, many showing a lumen. Lateral thyroids 
show no cavity: they touch wings of median thyroid. Tip of tongue free. Beginning 
differentiation of tongue muscle. 
Tympanic cavity quite distinct. Caudal end of thymus just cephalad of pericardial 
chamber. Thymus appears as one body in this region. Thyroid quite extensive; 
numerous bands of cells, many containing a lumen, with vascular mesenchyma 
between. Thyroid extends around region of larynx. Lateral thyroids, solid, on dorsal 
aspect of wings of median thyroid. ’ 
Tip of tongue freely projecting inside of edge of mandible. Tongue muscle in 
process of Rear, Small median raphe of tongue. Thymus, just cephalad of 
pericardial chamber, appears as one body; made up.of solid bands of cells with 
vascular mesenchyma between them. Thymus now quite large. 
Differentiation of tongue muscle well advanced. Median raphe of tongue. Thymus 
larger than at I8 days, now quite bulky, but in essentially the same condition. Thyroid 
large; composed of numerous cords of cells, many showing a small lumen. 
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