STUDIES IN MAMMALIAN EMBRYOLOGY. 489 



rig. 83 (1890) is the uterus of wliich a section is figured in fig. 7 (1893). 



65 (1890) corresponds to 



42 (1890) „ 



15 (1890) 



13 (1890) „ 



6 (1893). 

 5 (1893). 

 4 (1893). 

 3 (1893). 



On PI. 34 of this paper further stages of pregnaut uteri in 

 external view are figured. The numbers between crotchets 

 have reference to the catalogue number of the specimen ; and as 

 these numbers are also attached in red type to the transverse 

 sections of Pis. 31 and 32, it will be easy to compare these two 

 sets. The egg shape of the swelling (figs. 4 — 10) is seen to 

 be soon exchanged for a more pear-shaped one with a faint 

 constriction in the middle (figs. 11 — 13). The furthermost 

 projecting surface is the incipient placenta ; the swelling 

 closer to the mesometrium is that of the inverted yolk-sac 

 and of the growing embryo itself. This latter swelling very 

 soon is seen to increase at a more rapid rate than the former ; 

 in fig. 38 it has become somewhat triangular, the placen- 

 tal area projecting in knob-like fashion. The connecting 

 portions are yet very narrow tubular ducts. As pregnancy 

 advances further these portions are finally also widened out, 

 and in the fully ripe uterus the embryos are no longer sepa- 

 rated by such formidable constrictions as in the early stages, 

 the placental area having at the same time become much more 

 flattened out (figs. 44, 45). 



We now turn to the transverse sections, and the various 

 histological changes which accompany this transformation in 

 the outward shape of the uterus. 



In the stage of figs. 1 and 2, where the embryos are yet 

 contained in the oviduct, and where any outwardly visible 

 local swelling is not detectable, we see the uterine muscularis 

 still in its full thickness, the outer layer of fibres being longi- 

 tudinal (fig. 16), the inner circular. Inside of the muscularis 

 the mucosa is of very varying thickness, as can be gathered at 

 a glance from the figs. 1, 2, and 16. Close to the mesometrium 

 a folded epithelium without any uterine glands opening out 

 into the lumen is present, and separated by an inconsiderable 



