MUCOUS MEMBRANE. 



jpassages, as formerly described, the submu- 

 cous areolar tissue presents a remarkable mo- 

 dification, and is closely joined to the peri- 

 chondnum of the inner surface of the cartilages. 

 It is worthy of remark that the glands with 

 which the tra^heal portion of the membrane is 

 furnished, are not placed, like the buccal, 

 duodenal, and other similar glands, immedi- 

 ately subjacent to the mucous membrane, but 

 on the posterior surface of thetrachealis muscle, 

 which is pierced by their ducts. This peculiar 

 arrangement would seem to be accounted for 

 by the deviation from the ordinary form which 

 the submucous areolar tissue heie presents, 

 and which renders it ill adapted to give to these 

 irregular-shaped bodies that loose investment 

 which they everywhere possess, and which 

 therefore appears necessary to them. 



The mucous lining of the whole alimentary 

 canal below the cardia is the largest and best 

 marked example of what I have termed the 

 compound mucous membrane, being com- 

 posed of vertical tubes which are truly glands, 

 opening on the general surface. That of the 

 small intestine presents villi also. This entire 

 membrane is very soft and easily torn, because 

 its chief mass consists of an epithelium, the 

 particles of which adhere but slightly either to 

 one another or to the basement membrane, and 

 are everywhere disposed in a single layer. 

 There is moreover scarcely any areolar tissue 

 between its involutions, which have, therefore, 

 little besides the vascular web to sustain them. 

 The submucous areolar tissue is in considerable 

 abundance between the mucous and the muscular 

 coats. (See STOMACH and INTESTINAL CANAL.) 

 The lining membrane of the hepatic and pan- 

 creatic ducts is simple, and its epithelium of the 

 prismatic variety. 



In the genito-itrinary tract, the epithelium 

 presents every variety. The fossa navicularis* 

 is clothed with small, flat, or roundish scales, 

 the rest of the urethra with a single series of 

 prismatic particles. The cells of the prostate 

 are lined with spheroidal epithelium, the vasa 

 deferentia with prisms. In the vesiculae semi- 

 nales there is a pavement of somewhat flat- 

 tened granules, and also in Cowper's glands. 

 In the bladder, ureters, and pelves of the kid- 

 neys, the epithelium is in the form of longish 

 cells intermediate between the spheroidal and 

 the prismatic varieties. The nymphae, clitoris, 

 hymen, and vagina are covered with scaly epi- 

 thelium, and this has been noticed by Henle in 

 cases where the hymen has been entire. Within 

 the neck of the uterus the epithelium becomes 

 prismatic and clothed with cilia, and so con- 

 tinues over the surface of the uterus and Fal- 

 lopian tubes, and even for some distance over 

 the outer surface of their fimbriated extremities. 

 Beyond this it merges gradually into the com- 

 pressed cells of the serous membrane. The 

 lining membrane of the Fallopian tubes, as well 

 as that of the uterus, is of a compound nature, 

 especially during gestation, and consists of 

 tubules arranged vertically to the general sur- 

 face. It is to be- observed that the cilia only 



* Henle, lot. pit, 



VOL. III. 



clothe the general surface, and that the epithe- 

 lium lining the tubules is spheroidal, or inter- 

 mediate between that and the prismatic. It is a 

 form of the glandular variety, and bears no cilia. 



Of the glands. The varieties apparent in 

 these organs also may be explained by an ex- 

 amination of the modifications and modes of 

 aggregation of the elementary tissues already 

 mentioned. It may be said, in general terms, 

 that the glands are characterized by their solid 

 form, by the great preponderance of their epi- 

 thelial and vascular tissues, and by the small 

 quantity of their areolar tissue. It is rare for 

 this last to invest every individual involution 

 of the mucous surface in the interior of a gland ; 

 but it usually gives a common covering to the 

 whole organ, as well as less complete ones to 

 those subdivisions of it, termed lobes or lo- 

 bules, which result from the mode of distri- 

 bution of the bloodvessels and duct, and are 

 designed for the purposes of package or pro- 

 tection. 



Such an investment is usually termed the 

 proper coat or capsule of a gland, and seems 

 to correspond most nearly with the submucous 

 areolar tissue of the compound mucous mem- 

 brane, as, for example, that of the intestinal 

 canal. 



The propriety of these remarks will appear, 

 on a particular application of them. As I be- 

 fore entered somewhat in detail into the internal 

 composition of the liver, it may now be se- 

 lected for illustration. The epithelium, which 

 in the gall-bladder and larger ducts is of the 

 prismatic kind, becomes bulky and of a flat- 

 tened spheroidal form, in the lobules. It there 

 also acquires a peculiar character, viz. nume- 

 rous minute globules of an oily or fatty nature, 

 disseminated within the substance of each par- 

 ticle. The basement tissue seems to cease, 

 and on an examination of a thin section of the 

 lobule under a high power of the microscope, 

 its chief bulk appears to consist of epithelium. 

 There is scarcely a trace of areolar tissue to be 

 anywhere detected. Even the coats of the 

 capacious capillary bloodvessels, in the close 

 meshes of which the ultimate ramifications of 

 the bile ducts are situated, are with difficulty 

 seen, and are of extreme delicacy. The sub- 

 mucous areoiar tissue of the hepatic ducts, 

 with which the whole of the contiguous cap- 

 sule of Glisson should be associated, cannot, 

 when arrived at the lobules, be followed into 

 their interior. It can only be distinguished in 

 very slender quantity, giving them a partial in- 

 vestment, on those aspects which share in form- 

 ing the portal and hepatic-venous canals, and 

 where, in the angles of union between three or 

 more lobules, a terminal twig of the portal 

 vein runs up to open on all sides into their 

 capillary plexus. No lobule is isolated from 

 the rest by a complete capsule, but commu- 

 nicates immediately by its capillary network, 

 with those near it. The intralobular vein has 

 a similar want of areolar tissue around it; and 

 thus the main mass of the lobule, and of the 

 whole liver, consists of epithelium and a plexus 

 of capillaries. Those lobules, however, which 

 contribute to form the general surface of th* 



3 K 



