histology of' thf) oviduct of the domestic hen. 419 



Histology of the Uterus. 



There is no clear dividing line between the isthmus and the 

 uterus such as was described between the albumen portion and 

 the isthmus (p. 400). Instead the isthmus passes gradually 

 into the expanded uterus without any distinct break in the tissue 

 layers. As is clearly shown in figure 456 the character of the 

 longitudinal ridges in the uterus is quite different from that of 

 the homologous structures in any other portion of the duct — 

 in fact the ridges, as such, are lost and instead we find small 

 leaf like folds of the epithelium. The immediate cause of this 

 change in the character of the folds is probably a mechanical 

 one connected with the greater amount of surface to be covered. 

 If the same number (20 to 30) of ridges which are found in 

 the albumen portion and the isthmus were continued over the 

 expanded uterus they would lie rather far apart in this latter 

 region. The branching of the ridges and the refolding of the 

 intervening surface would account in some measure for the 

 change in the character of the folds. There may also be some 

 physiological reasons for this change since as we shall see the 

 character of some of the glands in the uterus differ from what 

 has ibeen found in the other portions of the duct. 



As shown in figure 468 the same muscle layers are present 

 in the uterus as in the more anterior regions. These layers, 

 particularly the outer, longitudinal muscles, are somewhat 

 thicker and better developed than in the regions previously dis- 

 cussed. However, there is but little difference in this respect 

 between the isthmus and the uterus. The connective tissue 

 layers present no change of any importance from the conditions 

 found in the anterior regions. Under low magnification the 

 cross section of the epithelial folds in the uterus do not differ 

 essentially in appearance from those found in the isthmus. The 

 folds, however, are not so high and perhaps on the average con- 

 tain a thicker layer of glandular tissue (tubular glands). The 

 epithelium covering these ridges presents the same general ap- 

 pearance as that found in the isthmus and albumen portion. 

 There is then no striking morphological differentiation in the 

 appearance of the tissue layers of the uterus which wouid indi- 

 cate its specific function of shell formation. The same layer 

 of tubular glands and as we shall see, the same ciliated, glandu- 

 lar epithelium occurs here as elsewhere. If any morphological 



