THE SECRETING MEMBRANES AND GLANDS. 



63 



closely the liquor sanguinis. for when collected in quantity it coagu- 

 lates. They are covered with a single layer of flattened scale-like 

 cells, constituting a very simple form of epithelial tissue, called the 

 squamous or scaly epithelium. Fig. 43, a. 



The synovial membranes lining the joints and the sheaths of tendons 

 somewhat resemble the serous membranes, forming like them closed 

 sacs ; but they are thicker, have a thicker epithelium, and secrete a 

 thicker fluid the synovia. They are sometimes provided with fringes 

 or projections, called, erroneously, glands (glands of Havers). Fig. 

 41, a, 1, 3. 



The mucous membranes do not form closed sacs, but open directly 

 or indirectly on to the surface of the body. The chief or most exten- 

 sive mucous membrane in the body is named the " gastro-pulmonary 

 mucous membrane," because it forms the lining membrane of the di- 

 gestive organs and the lungs. Another mucous membrane, of smaller 

 extent, lines the urinary passages and the cavities connected with 



Fig. 41. 



Fig. 41. (After Sharpey.) Three plans, a, b. c, of supposed sections of secreting membranes, to show the 

 general arrangement of their component structures, and the way in which their surfaces are increased. 

 In all three plans, the broad shaded line represents the areolo-vascular layer, the thin solid line is the 

 basement or limiting membrane, and the dotted line the epithelial or covering layer, a, shows an in- 

 crease by simple plaited or fringed projections, b, five modes oft increase by recesses, forming five kinds 

 of simple glands, viz. 1, a tubular follicle or crypt : 2, a saccular follicle or sac : 3, a coiled tube ; 4, a mul- 

 tilocular tube, that is, a tube with depressions in it ; 5, a multilocular sac. c, shows two forms of compound 

 glands; 6, branched tubes forming a compound tubular gland; 7, branched tubes ending in little recesses 

 or vesicles, forming a compound racemose or conglomerate gland. 



them. The former membrane commences at the mouth, extends into 

 the nose and between the eyelids, and into certain deep parts of the 

 ear, and then passes downwards through the air-tubes into the lungs, 

 and along the whole length of the alimentary canal. It is also ex- 

 tended in modified forms along the ducts of all the glands which open 

 upon it. The mucous membranes consist of a fibro- or areolo-vascu- 

 lar layer named the corium, generally limited at its surface by a very 



