INTESTIKE8. 



INTESTINES. 



npon the 

 with the 



____ i uid DM propulsion of their content* are effected; the 

 liiealiHilllHl flbres tending to shorten Moh portion of the cunM, while 

 the circular contract it* diameter ; and the two sets together pro- 

 ducing a motion of the tube somewhat like that of a worm, whence 

 it ha* received the name of vermicular motion. Ileneath these layer*, 

 and separated from them by a stratum of cellular tiasuc, which ha 

 bean sometimes called the fourth or nervous coat, U the mucous 

 membrane, which U the moet important part of the inteetinal canal. 



The structure of theee ooaU of the intestine* has been most care- 

 folly observed by means of the microscope. The minute structure of 

 the inUetinea corresponds to a considerable extent with what is met 

 with in the rtomtfb. There are however difference* of structure 

 especially in the mucous coat of the intestines. We shall describe first 

 the muscular structure, and in doing this we shall follow Professor 

 Kolliker in his ' Manual of Human Histology.' 



The muscular coat of the smaller intestines is somewhat thicker in 

 the duodenum and the upper portions, than in the lower ; it has in 

 geusul a thickoea* of \ f", and is composed only of longitudinal 

 and transverse fibres. The former are always less developed, and do 

 not form a continuous layer, since they are very few or entirely absent 

 the attachment of the mesentery ; they are usually most distinct 

 the free border, though even here they may be readily torn away 

 the serous membrane, so as at once to leave the second layer 

 exposed. The latter is complete and continuous, consisting of circular 

 bundles, which not uncommonly anastomose at very acute angles. 



In the large intestines the longitudinal fibres are reduced to the 

 three ligamenta coli, muscular bands of 4"' 6'", or even V' broad, 

 and I'" 4'" thick, which commencing upon the caecum are united 

 upou the tigmoid flexure into a single longitudinally fibrous layer, 

 thinner than in the small intestines, and more especially developed in 

 the duplicator**, which are known under the name of the plica; 

 ajgrnotdec. All the fibres belong to the smooth or non-striated 

 system of muscular fibres. Many of them present knot-like enlarge- 

 ment* and frequently zigzag flexures, which produce the transversely 

 striated appearance of the entire bundles of such muscles so fre- 

 quently met with in spirit preparations. The arrangement of the 

 fibre-ceil* in the different strata is simply this, mutually applied in 

 their length and breadth, and coherent: They are united into thin 

 muscular bands, which when invested with a coating of connective 

 tissue, and frequently also united into secondary bundles, constitute 

 the thicker or thinner muscular tunics of the different regions ; which, 

 again are surrounded and separated from the contiguous parts by 

 coostderabls layer* of connective tissue. 



Blood-vessrU are very abundant in the smooth muscles ; and their 

 capillaries, of 0-003'" 0-004'", constitute a characteristic network 

 with rectangular meshes. Nothing is known about the lymphatics ; 

 nor are the relations of the nerves yet ascertained, except that Kcker 

 has observed the division of fine nervous tubules in the muscular 

 tunics of the stomach of the frog and rabbit. 



The mucous membrane of the small intestines is thinner than that 

 of the stomach, but more complex in it* structure, inasmuch as 

 besides the tubular, or Lleberkuhnian glands it present* a great 

 number of permanent folds and villi, also imbedded in its substance, 

 peculiar closed follicles, the so-called solitary and Peyer's glands, and, 

 In the submncou* tissue of the duodenum, Brunner's glands. The 

 mucous membrane consists of connective tissue which is internally 

 ras, or indistinctly fibrillated ; except where certain gland* 

 i i* but little submucous tissue, so that it U pretty closely 

 with the muscular tunic. Upon the inner surface of the 

 nbrane there roils a cylinder-epithelium, whilst exter- 

 nally toward* the enbmucous tissue it is bounded by a layer of smooth 

 muscles discovered by Brucke, which measures at most 0-0177'". 

 They are disposed longitudinally and transversely, but in man their 

 alight development render* it often very difficult to discover them. 



The villi of the small inUstincs an small whituh elevation* of the 

 innermost portion of the mucous membrane, readily distinguishable 

 with the naked eye, and which distributed upon and between the 

 valtuUr ooonivente* through the whole extent of the small intestines, 

 from the pylorus to the sharp edge of the ileocoeoal valve, are set so 

 alas* tcfeihsr a* to give the mucous membrane it* well-known velvety 

 appearance. They are moet numerous (SO to 90 upon a square line) 

 in the duodenum and jejunum, lees so in the ileum (40 to 70 upou 

 a square line). In the duodenum they are broader and leas elevated, 

 resembling fold* and lamina -fa'" {" in height, ,"'4'" or even 

 I"' in breadth. In the j-junmu they appear for the most part 

 to be emiical and flattened; frequentlv they are even foliated or 

 cylindrical, clavate, or filiform, the three Utter form* predomi- 

 netinf In tho jejunum. The length of the villi i* from i"'- - 4'", the 

 bmdth from {'"fo", or even ft"', the thickness in the flattened 

 tonne ,V". 



The villi are composed of two portions, a deeper coat belonging to 

 the mucous membrane, and an epithelial superficial coat The contour 

 of the former, or villua proper, is similar to that of the entire villu* ; 

 it in imply a solid procees of the mucous membrane containing blood- 

 vemrls, lymphatic*, and smooth miiwles, whose matrix, through which a 

 variable number of roundiah nuclei are watteml, in general exhibits 

 no morphological peculiarity more decided than that of the mucous 

 membrane itself, yet must most undoubtedly be regarded a* a meta- 



morphosed connective tissue without any intermixture of elastic 

 tissue. The bloodvessels of the villi are so numerous that when 

 well injected those whose epithelium has been detached become 

 coloured throughout; and in living animal*, or in those which have 

 just been killed, each villus if viewed from above appears as a red 

 dot surrounded by a clear ring. In man every villus contains a close 

 network of capillaries of 0-003'" 0-005'", with rounded or elongated 

 nuclei, which lie* immediately beneath the homogeneous external 

 layer of the matrix, and is supplied by one, two, or three small arteries 

 of 0-01"' 0-016'". The blood is usually carried back directly into 

 the larger trunks of the submucous tissue by a vein of 0-022'", which 

 does not arise as in animals, by the arching round of the artery, but 

 proceeds from the gradual confluence of the finest capillaries. The 

 relations of the lacteals in the villi of man, have not hitherto been 

 perfectly made out ; for although the majority of investigators are 

 inclined, like the older observers, to suppose that they commence by 

 one or two coccal branches, yet recently several observers have con- 

 tended for the view that they originate in a filiform manner. On 

 this subject Professor Kolliker remarks that in the human subject he 

 has never succeeded in meeting with villi distended with chyle, and 

 in empty ones, he has been unable to obtain any decisive evidence ; 

 on the other hand, in animals, he feela certain that in many cases only 

 a single lacteal which has a coecal and frequently enlarged end, and 

 whose diameter U much greater than that of the capillaries, traverse* 

 the axis of the villus. He says he believes that all the narrow cylin- 

 drical and filiform villi will be found to present this condition, but 

 that, on the other hand, the number and mode of origin of the lacteal* 

 may possibly be different in the broad and foliaceous forms. 



In addition to these organs the villi also contain, aa Brucke dis- 

 covered a short time ago, a thin layer of longitudinal smooth muscles, 

 situated more centrally round the lacteals; these however are not 

 always distinct in man, they produce contractions of the villi, which 

 are very evident immediately after death, and which, according to 

 Brucke, are also perceptible ia the living animal. They have in all 

 probability an important influence over the propulsion of the chyle, 

 and of the venous blood in the villi always supposing that there is 

 no objection to the assumption that they perform repeated contractions 

 during life. Nothing is known of nerves in the villi. The epithelium 

 of the villi and of the rest of the surface of the mucous membrane, 

 although it is very intimately united with the deeper-seated parts 

 during life, only becoming detached accidentally or by disease, 

 separates very readily in the dead subject, and am only be observed 

 in perfectly fresh portions of intestine. It consists everywhere of a 

 simple layer of cylindrical cells slightly narrowed below of O'Ol"' 

 0-012'" in length and 0-003'" 0-004'" in breadth, whose contents are 

 usually nothing but fine granules, and an oval, clear, vehicular nucleus, 

 provided with one or two nucleoli. During life, these cells, which 

 agree in all their chemical characters with the deeper cells of the 

 oral epithelium, are so intimately united, that even after death their 

 contours in a longitudinal view, are at first either not at all or only 

 indistinctly distinguishable, though on the surface they have the 

 appearance of a beautiful mosaic. The cylinders only become quite 

 distinct when they are either spontaneously or artificially detached, 

 a process which usually takes place in such a manner that they hang 

 together in continuous portions, all the cells covering a villus, some- 

 times coming off together like the calyptra of a moss. 



The addition of water to these cells produces a separation of tho 

 cell-contents from the broad end, giving rise, in separate cells, to the 

 appearance of a membrane thickened upon one side, and, in series of 

 cells or entire villi, to that of a peculiar structureless coat, like the 

 cuticle of plants ; by its longer action, however, or by that of the 

 intestinal fluids, the bursting of the cells produces apertures in them, 

 or they become distended into large pyriform clear vesicles, 



We may here refer to the changes which the epithelial cells and 

 the villi in general undergo during digestion. The most striking 

 circumstance is the occurrence of fat-globules in different parts of tho 

 villi, which may always be observed tluring the formation of a fatty 

 milk-white chyle. The succession of the morphological steps is as 

 follows : The fat contained in the chyme at first enters only isolated 

 epithelial cells in different regions of the villi, so that in each we soon 

 observe a largo ovate shining drop. 



The number of these fat-cells rapidly increases, and then the villi 

 acquire a very peculiar appearance, often as if beset with pearls, from 

 the irregular alternation of cells filled with fat, and consequently 

 bright and shining, with those which are empty and pale. In the 

 end all the cells become filled with these drops, and the epithelium 

 appear* quite dark by transmitted, hut whitish by reflected light, 

 giving ita aspect to the whole villus. 



With the repletion of the entire epithelial covering of the villus, 

 absorption commences, but up to this time nothing has entered the 

 lacteals. This however soon takes place, and the first indication we 

 observe is tho breaking up of the large drops of fat in the cells into 

 many tolerably minute fatty molecules. When this has occurred, 

 these drops penetrate by degrees from all sides into the parenchyma 

 of the villuii itself, fill it morn and more, and at last enter the central 

 lacteal, whose whole length they eventually occupy. In the mean- 

 while, frenh fat has been continually passing in from the intestinal 

 canal, not in the form of large drops however, but henceforward in 



