Normal Plates of the Development of Necturus maculosus. 



27 



Nose 



Hypo- 

 physis 



Mouth 



Digestive System, Liver, 

 Pancreas, Spleen 



Com- 

 pressed ; 

 extended 

 laterally. 

 Contains 



many 

 tubules. 



Epithelium of pharynx con 

 sists of 2 or 3 layers of flat 

 cells containing numerous 

 unicellular glands. Oesopha- 

 gus thrown into numerous 

 longitudinal folds; epithe- 

 lium columnar, ciliated, with 

 unicellular glands. Muscular 

 wall very thin. Liver very 

 large. Lies on right side. 

 In frontal section outline is 

 long triangle, in transversa 

 section an equilateral tri- 

 angle. Posterior end shows 

 several irregulär processes. 

 Pancreas elongated cephalo- 

 caudallj'. Anterior portion 

 flattened and closely ap- 

 plied to dorso-mesial wall of 

 mtestine. Posteriorly greatly 

 thickened and roughly tri- 

 angulär in shape. Posterior 

 end lies on right side. 



Anterior wall of stomach 

 thin; circular band of inus 

 cular fibers very thin, in 

 creasing in thickness toward 

 pylorus. Epithelium colum- 

 nar. Submucosa developed. 

 Extreme anterior end free 

 from glands. Flask-shaped 

 glands confined to anterior 

 portion. Enlarged part of 

 glands consists of a Single 

 layer of very flat cells ; 

 duct, cuboidal or columnar. 

 Middle and posterior portion 

 of stomach contains bran- 

 ched tubulär glands. In 

 pyloric portion epithelium is 

 thrown into longitudinal 

 folds. Inner ends of cells 

 form a striated border which 

 extends into intestine. Liver 



contains numerous bile 



ducts. Hepatic cords well 



defined. Highly vascular. 



Gills. Thyroid, 



Thymus, Trachea, 



Lung 



Urino-genital 

 System 



Heart and Blood 

 Vessels 



Teeth 



project 



far into 



mouth 



cavity. 



Tongue 



narrower 



in front. 



Taste 

 buds well 

 devel- 

 oped in 

 epithe- 

 lium of 

 tongue. 



Intestine shows strong cir- 

 cular and longitudinal bands. 

 Walls thrown into longitu- 

 dinal folds. Lumen greatly 

 expanded at level of pos- 

 terior limbs forming rectum? 

 Epithelium columnar. Uni- 

 cellular glands more nu- 

 merous posteriorly. Gall 

 bladder large oval, extends 

 caudally beyond liver. Walls 

 formed of a single layer of 

 flat cells. Cystic duct large. 

 Pancreas composed of bran- 

 ched tubules. Dorsal portion 

 opens by a single duct just 

 caudally of stomach : ventral 

 portion smaller, opens by 

 two ducts. Spleen lies on 

 left side, in frontal or sagittal 

 section long, oval pointed in 

 front. Arrangement of cells 

 suggesting tubules. 



Gills all developed. Se- 

 cond, third and fourth 

 arches perforate, first 

 and fifth not broken 



through. Thyroid 

 small, halves widely 

 separated; consists of 

 20 — 30 large vesicles. 

 Lies close against first 

 epibranchial. Many 

 vesicles filled with 

 colloidal material. 

 Trachea at caudal end 

 much larger than Oeso- 

 phagus. Divides at 

 level of glenoid cavity. 

 Lungs much longer 

 extending some dis- 

 tance behind liver. 

 Right lung larger 

 than left and extends 

 further caudad. Epi- 

 thelium very thin 

 and flat. 



Skin 



Pronephros 



degenerating. 



Lumina of many 



tubules obliter- 



ated. Duct 



degenerating. 



Mesonephros 



extends from 9' 



or 10" Segment 



over about 



13 Segments. 



Müllerian duct 



not formed. 

 Bladder large, 

 wide transver- 

 sely, thin-wal- 

 led, extending 



well forvvard 



beyond pelvis 



Sexual glands 



nearly coexten- 



sive with 



mesonephros 



Heart well developed. 

 Auricles well defined 

 folded over ventricle. 

 Imperfect ventricular 

 septum. Ventricle with 

 numerous muscular tra- 

 beculae. Truncus arte- 

 riosus thick walled : conus 

 thin. Branchial arteries 

 well developed. Pulmo- 

 nary arteries and veins 

 very small. Hepatic veins 

 very large; they unite to 

 form sinus venosus which 

 erapties into the right 

 auricle. Internal and 

 external jugulars present; 



jugular sinus well 



marked. Splenic, gastric 



and mesenteric veins 



formed. Caudal vein 



gives off' branches to 



form renal portal system. 



Arteries and veins in 



limbs complete. 



Skeleton Limbs Stage 



Internasal cartilage 



well defined. 

 Lateral and dorsal 

 wall of brain Cap- 

 sula now a thin 

 layer of bone. Bone 

 in whole extent of 

 lower jaw. Nasal 

 capsule formed in 



cartilage. Hypo- 



hyal much larger. 



Second hypobran- 



chial still very 



small. Cartilage 

 appearing around 

 orbit. Membrane 



bones of skull 

 generally formed. 

 Tibia and fibula, 

 tarsals and meta- 



tarsals ossified. 



48 



48 a 



49 



4* 



