BEPBOD ( '( 'T/ON. 457 



tions. Its thick walls consist largely of plain muscular tissue arranged 

 roughly in the form of three indistinctly marked layers. Of these, the exter- 

 nal and the middle coats are thin ; the fibres of the former are arranged in 

 general longitudinally, those of the latter more circularly and obliquely. 

 The third, most internal layer, which is regarded by some as a greatly hyper- 

 trophied muscularis mucosae, forms the greater part of the uterine wall. Its 

 fibres are arranged chiefly circularly ; toward the upper part they become trans- 

 verse to the Fallopian tubes, and at the cervix longitudinal fibres lie within 

 the circular ones. The individuality of the muscular layers and uniformity 

 in the course of the fibres is largely interfered with by the numerous blood- 

 vessels of the uterine walls. The uterus is lined by an epithelium composed 

 of columnar ciliated cells, except in the lower half of the cervix, where a stratified 

 non-ciliated epithelium exists. The direction of the ciliary movement in woman, 

 as in other mammals, is toward the os uteri. 1 The mucous membrane is thick, 

 and contains very numerous, branching, tubular glands, which are lined by 

 ciliated epithelium and have a tortuous course, terminating in the edge of the 

 muscular layer. They secrete a viscid, mucous liquid. Between the glands 

 are branched connective-tissue cells, which are not unlike the connective-tissue 

 cells of embryonic structures, and wandering cells. Lymph-spaces and bl< >o< 1- 

 capillaries exist. The development of the tissue goes on slowly up to the 

 time of puberty, and, as we shall see, after puberty the mucous membrane is 

 subject to constant change. 



Menstruation. — Except during pregnancy the most striking activities of 

 the uterus are associated with that peculiar female function which, from its 

 monthly periodicity, is called menstruation. The most obvious external fact 

 of this phenomenon is the discharge every month of a bloody, mucous liquid 

 through the vagina ; the most obvious internal facts are the bleeding and the 

 degeneration and disappearance of a portion of the mucous membrane of the 

 body of the uterus. This curious process, though having analogies in lower 

 animals, occurs most markedly in the human female, and from before the time 

 of Aristotle to the present, among both primitive and civilized races, its signifi- 

 cance has been the cause of much speculation. The detailed phenomena of 

 menstruation are not as well known as they should be. Experimentation is 

 practically out of the question, and the opportunities of careful post-mortem 

 study of normal healthy uteri at different stages are rare. The main facts arc 

 as follows : 



Some days before the flow occurs the mucous membrane of the body of the 

 uterus begins to thicken, partly by an active growth of its connective tissue 

 elements and partly by an excessive filling of its capillaries and veins with 

 blood. The cause of this swelling is not known. It continues until the 

 membrane has doubled or trebled in thickness, and, according to some authori- 

 ties, the uterine cavity becomes a mere slit between the walls. Then occurs an 

 infiltration of blood-corpuscles and plasma, probably largely by diapedesis, 

 although possibly assisted by rupture, through the walls of the swollen capil- 



1 Hofmeier : Citilralhlnlf j'iir ihjuiikolixjic, lS'.t.'i, xvii. S. 7<>l. 



