THE MUCOUS MEMBRANE. 



1145 



SYNOVIAL MEMBRANES. 



Synovial membranes, like serous membranes, are connective-tissue membranes 

 placed between two movable tissues, so 

 as to diminish friction, as in movable 

 joints; or between a tendon and a bone, 

 where the former glides over the latter; 

 and between the skin and various subcu- 

 taneous bony prominences. 



The synovial membranes are composed 

 essentially of connective tissue, with the cells 

 and fibres of that structure, containing numer- 

 ous vessels and nerves. It was formerly sup- 

 posed that these membranes were analogous 

 in structure to the serous membranes, and 

 consisted of a layer of flattened cells on a 

 basement-membrane. No such continuous 

 layer, however, exists, although here and 

 there are patches of cells probably epithelial 

 in nature. They are surrounded and held 

 together by an albuminous ground-substance. 

 Long villas-like processes (Fig. 685) are 

 often found projecting from the surface of 

 synovial membranes ; they are covered by 

 small rounded cells, and are supposed to 

 extend the surface for the secretion of the 

 fluid which moistens the membranes, and 

 which is named synovia. It is a rich lymph, 

 plus a mucin-like substance, and to the latter 

 constituent it owes its viscidity. A further 

 description of the synovial membranes will be found in the descriptive anatomy 

 of the joints. 



FIG. 685. Villus of synovial membrane. 

 (After Hammar). 



MUCOUS MEMBRANE. 



Mucous membranes line all those passages by which the internal parts com- 

 municate with the exterior, and are continuous with the skin at the various orifices 

 of the surface of the body. They are soft and velvety, and very vascular, and 

 their surface is coated over by their secretion, mucus, which is of a tenacious con- 

 sistence, and serves to protect them from the foreign substances introduced into 

 the body with which they are brought in contact. 



They are described as lining the two tracts the gastro-pulmonary and the 

 genito-urinary ; and all, or almost all, mucous membranes may be classed as 

 belonging to and continuous with the one or the other of these tracts. 



The deep surfaces of these membranes are attached to the parts which they 

 line by means of connective tissue, which is sometimes very abundant, forming a 

 loose and lax bed, so as to allow considerable movement of the opposed surfaces 

 on each other. It is then termed the submucous tissue. At other times it is 

 exceedingly scanty, and the membrane is closely connected to the tissue beneath ; 

 sometimes, for example, to muscle, as in the tongue ; sometimes to cartilage, as 

 in the larynx ; and sometimes to bone, as in the nasal fossae and sinuses of the 

 skull. 



In structure a mucous membrane is composed of corium and epithelium. The 

 epithelium is of various forms, including the squamous, columnar, and ciliated, 

 and is often arranged in several layers. This epithelial layer is supported by the 

 corium, which is analogous to the dermis of the skin, and consists of connective 

 tissue, either simply areolar or containing a greater or less quantity of lymphoid 



