182 THE ESSENTIALS OF HISTOLOGY 



developed. After persisting for a time it gradually shrinks and disap- 

 pears, but it becomes larger and remains longer persistent in the event 

 of pregnancy supervening. 



The Fallopian tubes are chiefly composed of plain muscular tissue 

 disposed circularly. They are lined by a mucous membrane which is 

 covered with ciliated epithelium. Externally they are covered by a 

 serous coat, within which is a thin layer of longitudinal muscular fibres 

 overlying the circular fibres. 



The uterus is usually described as composed of two parts, the body 

 and cervix. The wall of the uterus is formed of the following layers : 



1. A serous layer, derived from the peritoneum, which covers the 

 greater part of the fundus. 



2. A muscular layer, which is of considerable thickness and is 

 composed of plain muscular fibres disposed in two imperfectly separated 

 strata. Of these the outer is much the thinner, and its fibres are dis- 

 posed partly longitudinally, partly circularly. The inner muscular 

 layer, on the other hand, is very thick ; its fibres run in different direc- 

 tions, and it is prolonged internally into the deeper part of the mucous 

 membrane, the extremities of the uterine glands extending between 

 and amongst its fibres. It is imperfectly separated from the thinner 

 external layer by the ramifications of the larger blood-vessels, and 

 probably represents a much-hypertrophied muscularis mucosse. 



3. A mucous membrane, which is very thick and is composed of soft 

 connective tissue containing a large number of spindle-shaped cells. It 

 contains long, simple, tubular glands (fig. 219), which take a curved or 

 convoluted course in passing through the membrane. They are lined 

 by ciliated epithelium continuous with that which covers the inner 

 surface of the mucous membrane. In the cervix the mucous membrane 

 is marked by longitudinal and oblique ridges, and the glands are shorter 

 than those of the body of the uterus. Near the os uteri the epithelium 

 becomes stratified and overlies vascular papilla? of the corium. The 

 mucous membrane is exceedingly vascular, and it also contains a large 

 number of lymphatic vessels. 



At each menstrual period the greater part of the mucous membrane 

 of the body undergoes a process of disintegration accompanied by an 

 escape of blood from the capillaries of the membrane. This is suc- 

 ceeded by a rapid renewal of the membrane. Should gestation super- 

 vene, the process of renewal results in the formation of a greatly 

 thickened mucous membrane, with long convoluted glands, which is 

 then known as the decidua. 



The mammary gla ds are compound racemose glands which open 

 by numerous ducts upon the apex of the nipple. The ducts are dilated 

 into small reservoirs just before reaching the nipple. If traced back- 

 wards, they are found as in other compound racemose glands to com- 

 mence in groups of saccular alveoli. The walls of the ducts and alveoli 

 are formed of a basement-membrane lined by a simple layer of flattened 

 epithelium (fig. 220, A]. But during lactation, when the gland is in 



