CYCLIC CHANGES IN THE OVARIES AND UTERUS OP THE SOW, ETC. 135 



III. UTERUS. 

 GENERAL DESCRIPTION OF THE SOW'S UTERUS. 



During the period of sexual maturity the sow's uterus undergoes regular alter- 

 nations of structure, correlated with the ovarian cycle, which are continuously in 

 progress and are varied in their course only by the occurrence of pregnancy. These 

 alternations involve changes in the degree of surface folding of the mucosa, in the 

 morphology and dimensions of the surface epithelium, in the dimensions of the cells 

 of the superficial gland tubules, in the division rate of all the epithelial elements, 

 in the number and kind of wander-cells in the subepithelial portions of the stroma, 

 and in the amount of fluids in the interstices of the stroma. In the following pages 

 these changes will be followed in detail. 



The general structure of the cornual portions of the sow's uterus is illustrated 

 in plates 3 and 4. There is a lining epithelium resting upon a stroma of con- 

 nective tissue, and this in turn is seated directly upon the muscularis, which, as 

 usual in tubular forms of the uterus, is disposed in two layers, the inner circular and 

 the outer longitudinal. Into the stroma pass a large number of glands having 

 openings in the epithelium. 



The epithelium is fundamentally of a simple one-layered type, but (as we shall 

 see) the columnar arrangement is greatly modified at one period of the cycle, so 

 that some histologists (for instance Schmaltz, 1911) have even described it as 

 "many-layered." We may suspect that there is a good deal of incompleteness in 

 the descriptions of the uterine epithelia of other mammals, due, as in this case, to 

 lack of an understanding of the cyclic changes. 



The glands open into the uterine lumen by means of tubules which run more 

 or less directly, with but little branching and slight tortuosity, until they are well 

 into the stroma, when they begin to branch rather freely and to exhibit marked 

 tortuosity. In this way the mucosa is divided into two fairly well marked layers, 

 the superficial zone containing but few glands and the basal zone densely packed 

 with glands so twisted and involved that in sections they are cut across in every 

 imaginable way. There is a slight difference between the cells lining the glands of 

 the two zones; those of the superficial tubules are higher, measuring usually 15 to 

 25 micra in height as against 12 to 18 micra in the glands of the basal zone. There 

 is thus a greater proportion of cytoplasm to nucleus in the cells of the superficial 

 tubules, and they look larger and clearer than those of the smaller and deeper-lying 

 glands. Furthermore, the lumina of the superficial tubules are usually about 

 twice as wide as those of the basal glands, as might be expected from the probability 

 that many of the latter are drained by a few of the superficial tubules. There are no 

 permanent shorter glands or crypts, as in the uterus of the dog and other carnivores. 



There are no ciliated cells in the surface epithelium of the sow's uterus, but 

 cilia begin to appear immediately within the necks of the glands (fig. 17, pi. 2), 

 and may be found throughout the glands. They are better observed in the larger 

 superficial tubules, not only because they are more easily seen in the wider lumina, 

 but also because they are larger, stouter, and more numerous here. One may 



