140 T. THOMSON FLYNN 



cells eoutainiiig ijigment in the form of black streaky and 

 granular deposits. These cells occur throughout the whole 

 wall of the uterus. They are very abundant in the serosa 

 and are found distributed through the muscularis, the connec- 

 tive tissue, and the glandular epithelium. Such pigmented 

 cells have often been noted in the virginal and pregnant uteri 

 of Euth«^rian mammals. 



Foetal Structures. — In general the arrangement and 

 histology of the foetal membranes are in agreement with the 

 description given by Hill, and I find 1 can add nothing of 

 importance to his description of these structures. 



Allantois. — The vesicular portion of this is a somewhat 

 flattened body, taking, however, a curved shape corresponding 

 to the dorsal curvature of the trunk of the embryo. In surface 

 view it is somewhat elliptical, measuring 5 mm. by 3-1 mm. 

 The point of attachment of the stalk is placed a little nearer 

 the posterior than to the anterior end of the vesicle. The 

 difference in thickness and texture between the placental and 

 coelomic surfaces of the allantois is easily seen wdth the naked 

 eye. The coelomic surface is an extremely tenuous sheet 

 bearing the larger Idood-vessels, while the outer or allantoic 

 surface is more opaque and abundantly supplied with a network 

 of capillaries derived from or supplying vessels which pass round 

 the margin in the manner described by Hill. For a full descrip- 

 tion of these allantoic vessels I would refer the reader to Hill's 

 account. The allantoic stalk has the usual relations and 

 structure. 



Fixation of the Embryo. 

 • The importance of this stage rests on the fact that, over 

 a very small area, the trophoblast is now attached to the 

 thickened maternal syncytium (trophospongia). This 

 portion of the foetal ectoderm is, of coiirse, the outer layer 

 of the chorion, which consists, in addition, of somatic meso- 

 derm. The latter is a thin mesothelial layer consisting of 

 flattened cells with oval, somewhat deeply-staining, nuclei. 



The chorionic ectoderm typically consists also of a single 

 cell-layer as it undoubtedly does in the marginal free portions. 



