434 THE FEMALE REPRODUCTIVE ORGANS 



The connective tissue cells and fibres are frequently arranged in 

 membranous bands which extend lengthwise of the cord and in 

 transections present a peculiar concentric arrangement, the deli- 

 cate membranes alternating with broad tissue spaces, and often 

 inclosing the blood vessels or forming incomplete concentric 

 lamellae about the circumference of the cord. The surface of the 

 cord is clothed with an ectodermal layer of flattened epithelium 

 which occasionally forms several layers of cells. 



The umbilical vessels, the veins as well as the arteries, are 

 peculiar in that they possess unusually thick muscular walls. 

 Their smooth muscle fibres are disposed both longitudinally and 

 circularly. In transection the endothelial lining of the vessels is 

 seen to be thrown into prominent folds by the contraction of the 

 thick muscular wall. 



Remnants of the allantois, and occasionally of the yolk sac as 

 well, are found in the fetal end of the umbilical cord even at full 

 term. These appear in the form of indistinct epithelial tubes or 

 columns, whose cells often show evidences of degenerative changes. 



THE VAGINA 



The vagina is a fibro-muscular sheath whose wall is divisible 

 into three coats mucous, muscular, and serous. 



The mucous membrane is clothed by a layer of stratified squamous 

 epithelium, and is thrown into numerous folds or rugae. The epi- 

 thelium rests upon a fibrous basement membrane. The tunica pro- 

 pria is formed by a close-meshed areolar tissue which, in its deeper 

 and looser portion, is permeated by vascular channels of consider- 

 able size. This deep vascular layer is frequently described as a 

 submucosa; it rests directly upon the muscular wall. The sur- 

 face of the mucosa presents numerous conical papillae which pro- 

 ject well into the epithelial layer. 



The musculature of the vagina contains smooth or involuntary 

 fibres, and is divisible into an inner circular and an outer longi- 

 tudinal layer. The muscle fibres are long and slender. Consid- 

 erable connective tissue is distributed among the muscle bundles. 

 The latter are arranged in more or less parallel layers which are 

 united by the delicate bands of connective tissue. 



The outer fibrous coat consists of dense areolar tissue which is 

 well supplied with elastic fibres. It loosely unites the vaginal 

 wall to the surrounding tissues. In this coat is a plexus of blood- 

 vessels and lymphatics, from which branches pass to the muscular 



