ANATOMY. 



thin transparent basement membrane, which again is covered by a 

 layer of epithelial tissue. They are always of a deep red color during 

 life, owing to their vascularity ; but being thick and somewhat opaque, 

 as compared with the serous or synovial membranes, they often have 

 a pale pinkish brown hue after death. Sometimes a mucous mem- 

 brane is thin and smooth, as within the nose and air-passages, or it 

 may be thicker, as inside the cheek and throat. Sometimes it is pap- 

 illated, that is, covered with eminences called papillce, as on the tongue; 

 or villous, that is, provided with softer projections called villi, as in 

 the small intestine ; or it may be thrown into rugce or ridges, as in 

 the stomach, or developed into folds or valves, as in the small intes- 

 tine. In some places the mucous membranes are recessed into little 

 tubes, follicles or sacs, simple or branched, Fig. 41, b, c, and so form 

 minute glands; or, this formation of branched recesses being carried 

 to an immense extent, larger compound glands are formed. 



The mucous membranes secrete a slightly viscid moisture called 

 mucus; and from their simple or complicated glandular recesses are 

 formed all the varied kinds of secretions, such as the saliva, bile, 

 gastric juice, tears, &c., excepting only those which come from glands 

 similarly constructed, but existing in connection with the skin, such 

 as the sweat glands, the sebaceous glands, and the mammary glands. 



The different methods and degrees in 

 which the surfaces of secreting membranes 

 generally, are multiplied within a given 

 space, are illustrated in the plans shown 

 in Fig. 41, the description of which should 

 now be referred to. 



The simple and fringed projections, a, 1 

 and 3, occur in the synovial membranes; 

 the plaited form, 2, in the interior of the 

 eyeball. The simple forms of glands, b, 

 1 to 5, viz., the short tubule, follicle, or 

 crypt, the wide follicle or sac, the long coiled 

 tubule, the multilocular tubule, and the 

 multilocular sac, are met with in special 

 organs, which we shall have hereafter to 

 describe, as in the stomach, intestines, eye- 

 lids, nose, ear, and skin. The compound 

 forms of glands, c, are represented by the 

 kidneys, 6, and by the mucous, lachrymal, 

 salivary, and other glands, 7. A good ex- 



culus of an ostrich, b (after Kolliker), 



section through the substance of the 



Fig. 42. 



and the little rounded vascular bodies, 

 caiied the giomeruii, connected with the 



tubnli. C (Mnller), minute portion of 

 the parotid gland injected with mercury, 



to show its terminal ducts and vesicles, 

 AII the figures are slightly magnified. 



follicles from the prOVCntriCuluS, Or Secret- 



ing part of the stomach of the ostrich, 

 jf* 42, ; an instance of a compound or 

 branching tubular gland is seen in the nu- 

 man kidney, b ; whilst the ultimate lobules 



of galivary g]and ff with their terminal 

 . i -i / 



ducts and vesicles, form a good example 

 of a compound racemose vesicular gland, 



