GLANDS OF MUCOUS MEMBRANES. 409 



bladder, and on a finer scale in the vesiculae seminales ; still more minute alveolar 

 recesses with intervening ridges may be discovered with a lens on the mucous 

 membrane of the stomach. 



Glands of mucous membranes. Many, indeed most, of the glands of the 

 body pour their secretions into the great passages lined by mucous membranes ; but 

 there are certain small secreting glands which may be said to belong to the mem- 

 brane itself, inasmuch as they are found in numbers over large tracts of that mem- 

 brane, and yield mucus or special secretions known to be formed in particular 

 portions of the membrane. Omitting local peculiarities the glands referred to may 

 be described as of two kinds, viz. : 



I. Simple tubular glands (crypts). These are minute tubes formed by recesses 

 or inversions of the basement membrane, and lined with epithelium (fig. 465, gl). 

 They are usually placed perpendicularly to the surface and often very closely 

 together, and they constitute the chief substance of the mucous membrane in those 

 parts where they abound, its thickness depending on the length of the tubes, which 

 differs considerably in different regions. The tubes open by one end on the surface ; 

 the other end is closed, and is either simple or cleft into two or more branches. 

 Such tubular glands are abundant in the stomach, and in the small and large 

 intestines, where they are comparatively short and known as the crypts of Lieber- 

 kiihn. They exist also in considerable numbers in the mucous membrane of the 

 uterus, when they are longer and tend to be convoluted. 



II. Small racemose glands. Under this head are here comprehended minute 

 glands of the racemose or acino-tubular kind, which open on the surface of the 

 membrane by a longer or shorter duct. Numbers of these, yielding some a mucous, 

 others a more albuminous or watery secretion, open into the mouth. To the naked 

 eye they have the appearance of small solid bodies, often of a flattened lenticular 

 form, but varying much both in shape and size, and placed at different depths below 

 the mucous membrane on which their ducts open. They are also met with 

 throughout the pharynx and gullet and in the larynx, trachea, and bronchial tubes, 

 but in all these parts their secretion is purely of a mucous character. The glands of 

 Brunner, which are met with in the submucous tissue of the duodenum, near its 

 junction with the stomach, also bear a superficial resemblance to the racemose 

 mucous glands, and in minute structure they are not unlike them, but the nature of 

 their secretion appears to be different. 



The several mucous membranes are described more in detail when the organs of which they 

 form a part are treated of, and the works which refer to them may then also be mentioned 

 most appropriately. 



