454 THE PHYSIOLOGY OF REPRODUCTION 



the uterus. The glands are dilated, and their proliferated endo- 

 thelium forms a symplasma which blocks the lumina. At these 

 places the trophoblast advances more quickly, as if the resist- 

 ance was weaker, and the line of attachment is undulating 

 (Fig. 129). The dips thus correspond to the gland orifices and 

 represent the beginnings of the future villi. The blood-vessels are 

 large and numerous and have no adventitia, i.e. they are wholly 

 capillaries. But the more deeply placed of them acquire an 

 adventitia, the perivascular sheath (Masquelin and Swaen 1 ). It is 



FIG. 129. Thickened ectoderm (ectoplacenta) in the rabbit, attached to 

 placenta! lobe and dipping more deeply at the position of the glands. 

 (Chipman.) 



Ftetal ectoderm ; /, line of attachment of ectoderm ; d, fostal ectoderm 

 dipping into placental gland ; <7, terminal cul-de-sac of placental gland. 



formed of one or two layers of large connective tissue cells which 

 represent the first appearance of the decidual cells. After the 

 destruction of the superficial and glandular epithelium, the tropho- 

 blast advances into the interglandular tissue, the cells of which 

 degenerate in turn and are absorbed. The advance is most rapid 

 where a capillary is met with. 



The mucous membrane is now differentiated into two zones, the 

 intermediary region and the region of the uterine sinuses (Uuval). 

 The intermediary region lies superficially. It is closely packed with 

 fusiform stroma cells and capillaries with thin perivascular sheaths 



1 Maaquelin and Swaen, " Developpement du placenta maternel chez le lapin" 

 A'"//. / r.\cad. Roy. de Belg., 1879. 



