362 



HISTOLOGY 



Mucosa. 



Muscularis. 



described them. Toward the external orifice of the uterus the epithelium 

 becomes stratified and squamous, and rests on connective tissue papillae. 

 Thus it resembles the lining of the vagina of which it is a continuation, 

 and after the first child-birth it extends further up into the cervix than 

 before. 



The musculature of the uterus is a thick investment of interwoven 

 bundles which cannot be subdivided into well-defined layers (Fig. 366). 

 It begins immediately outside the tunica propria, and its inner portion 

 has been regarded as "an immensely hypertrophied muscularis mucosae." 



Further out there is a zone 

 containing many blood 

 vessels, which according to 

 this interpretation marks 

 the position of the submu- 

 cosa (Schafer). Accord- 

 ing to Henle and Stohr, 

 these vessels belong with 

 the middle of three muscle 

 layers, which is named, 

 therefore, the " stratum 

 vasculare." It is the 

 thickest of the layers and 

 its fibers are chiefly circu- 

 lar. The innermost layer 



or "stratum submucosum" 

 (Stohr) consists principally 

 of longitudinal fibers. The 

 outermost layer or "stra- 

 tum supravasculare" contains circular fibers internally and longitudinal 

 fibers externally. Some of the latter are continuous with the longitudi- 

 nal fibers of the uterine tubes; others are said to enter the round liga- 

 ments, which contain also some striated fibers; and still others spread 

 into the broad ligaments. 



In the cervix the three strata of muscle fibers are found to be very 

 distinct inner and outer longitudinal, and middle circular. Although 

 the uterus generally contains few elastic fibers, found only in its peripheral 

 layers and running perpendicular to the plane of contraction of the muscles, 

 elastic fibers are abundant in this position in the lower segment of the 

 corpus and vaginal portion of the uterus. During the first half of preg- 

 nancy both elastic and muscular fibers increase in size and number; 

 in the second half, the elastic fibers decrease in the musculature, but 

 increase in the perimetrium (Stohr). The way in which the thick layer 

 of muscles in the resting uterus becomes arranged in the thin layer of 



FIG. 366. FROM A TRANSVERSE SECTION OF THE MIDDLE OF 



THE UTERUS OF A GIRL FIFTEEN YEARS OLD. X 10. 



a, Epithelium; b, tunica propria; c, glands; I, inner muscular 



layer; 2, middle muscular layer; 3. outer muscular layer. 



