
PLACENTATION OF THE SEALS. 295 
There can be no doubt, however, from its position and structure, that this 
layer is the mucosa of that part of the uterus which corresponds to the 
placental zone; for it and the intra-placental lamine and trabecule are merely 
a more advanced condition of the crypt-like modification of the mucosa, which 
I have described in the earlier stages of placental formation in this animal. Is 
the whole thickness of the mucosa corresponding to the placental zone shed 
along with the placenta, or is this layer merely the superficial part of the 
membrane, are questions which may now be asked? These, of course, can 
only be satisfactorily answered after the uterus of a cat killed immediately 
after parturition has been examined. But I may state that, in the uterus of the 
cat in the mid-period of gestation, I found, on peeling off the placenta, that the 
serotina did not split into two layers,—one, a deciduous serotina attached to 
the placenta; the other, a non-deciduous serotina remaining connected to the 
uterine wall, but that the whole thickness of the serotina came away with the 
placenta, leaving the muscular coat exposed ; moreover the uterine surface of 
the placenta presented a smooth surface precisely similar to that exhibited by 
the organ when shed at the full time. A similar separation also took place 
more than once in the process of injecting the vessels of the gravid uterus. 
Though the placenta in the bitch, as in the cat, possesses the zonary form, 
yet its minute structure in the two animals presents sufficient differences to 
enable the anatomist readily to distinguish one from the other. If the descrip- 
tion and figures by SHARPEY and Biscuorr, of the early stages of formation in 
the bitch, be compared with the corresponding stages in the cat, a close resem- 
blance is seen; but in the more advanced stages, characteristic differences can 
be recognised. 
In the Bitch, both at half and full time, when the placenta was stripped off 
the uterine zone, a distinct mucous membrane was left on the uterus, which 
was continuous at the margins of the zone with the narrow band of decidua 
reflexa, and through it with the mucosa covering the non-placental area. This 
zonary mucous membrane was subdivided into numerous, irregularly polygonal, 
pits or trenches, bounded by folds of the mucous membrane ; which folds had 
a ragged, flocculent appearance. The membrane was very vascular, and at the 
ragged edges of the folds numerous torn blood-vessels were seen. When 
examined microscopically the free surface, not only of the pits and trenches, 
but of the folds, was seen to be covered by a layer of cells—the epithelium 
of the mucous membrane—which rested on the vascular sub-epithelial connec- 
tive tissue. When this epithelium was looked at from the surface, a pattern 
of polygonal cells was seen like the free ends of columnar epithelium ; but the 
cells were bigger than one usually finds this form of epithelium to be, and 
had, more especially in the uterus at full time, a distinct yellow colour, as if the 
cells were undergoing fatty degeneration. When the cells were scraped off, 
VOL. XXVII. PART III. 4H 
