4oS A Tliree Weeks' Human Embryo 



N. /I/-Z/Z.— Nerves III-XII. 

 nas. ep. — Nasal epithelium. 

 neur. or neurop. — Neuropore. 

 neph. or neph. t. — Nephric tubule. 



obi. 1-9. — Oblongata folds, 1 to 9. 

 ces. — Esophagus. 

 olf. — Olfactory epithelium or olfactory fold. 



pron. t. — Pronephric tubule. 



s. venosus. — Sinus venosus. 



sec. — Section. 

 sept, trans. — Septum transversum. 

 stom. — Stomach. 

 str., stri. — Striatum. 

 supra-ren. — Supra-renal capsule, adrenal. 



1. 1-21. — Mesonephrlc tubules, i-21. 



V. jug. — Vena jugularis. 



y. postcard, or Y. pc. — Vena cardinalis. 



V. umh. — ^Vena umbilicalis. 



Y. vit. — Vena vitellina 



vent. — ^Ventricle. 



vit. ves. — Vitelline vesicle. 



W. d.. Wolff, d.. Wolffian d.— Wolffian duct. 



EXPLANATION OF PLATES. 



Figures 1-13. 



Drawings made from a model of Embryo 148 of the Mall collection, with 

 sections and dissections of the same (see above. Models and Drawings). 

 Magnification of the figures, X SZVs- 



Plate I. 



Figs. 1 and 1a. View of the left side of the model. Compare with figures 

 of this embryo in articles by Mall 1, 5. 



It shows: The head comparatively small in diameter but great in length, 

 and forming at the neck-bend an angle of 65° with the body; the position of 

 the neuropore; the eye and ear scarcely apparent as external features; the 

 prominent heart, limb buds, and tall; the umbilicus turning to the right 

 (cf. Fig. 5); the wide undeveloped mouth and small maxillary process; the 

 crowding of the 2d, 3d, and 4th clefts into the precervical sinus; and 29 

 myotomes, the 3d being noted as the 1st cervical. 



The density of the stippling on Fig. 1 indicates the relative thickness of 

 the epithelium (see above. External Form). 



The topographic lines show the direction of the sections, the numbers 



