GLANDS 223 



The ovary is a ductless gland, the specific secretion of which, 

 the ovum, is under normal conditions taken up by the oviduct and 

 carried to the uterus. This is known as a dehiscent gland. 



Other ductless glands, such as the thyreoid, hypophysis and 

 adrenal, are known as glands of internal secretion, their specific 

 secretions passing directly into the blood or lymph systems. 



A few glands, e.g., the liver and pancreas, have both an internal 

 secretion, and an external secretion. 



General Structure of Mucous Membranes 



The alimentary tract, the respiratory tubules, parts of the genito- 

 urinary system, and some of the organs of special sense are Kned by 

 mucous membranes. While differing as to details in different organs, 

 the general structure of all mucous membranes is similar. The 

 essential parts are (i) surface epithehum, (2) basement membrane, 

 and (3) stroma or tunica propria. The epithelium may be simple 

 columnar, as in the gastro-intestinal canal; ciUated, as in the bronchi; 

 stratified squamous, as in the oesophagus, etc. The epithelium rests 

 upon a hasement membrane or membrana propria which, Uke the same 

 membrane in glands, is described by some as a product of the epithe- 

 hum, by others as a modification of the underlying connective tissue. 

 Beneath the basement membrane is a connective-tissue stroma, or 

 tunica propria. This usually consists of loosely arranged fibrous 

 tissue with some elastic fibres. It may contain smooth muscle cells 

 and lymphoid tissue. 



In addition to the three layers above described there is frequently 

 a fourth layer between the stroma and the underlying connective 

 tissue. This consists of one or more layers of smooth muscle, and 

 is known as the muscularis mucoscB. 



A mucous membrane usually rests upon a layer of connective 

 tissue rich in blood-vessels, lymphatics, and nerves — the submucosa. 



