4U3 



MUCOUS MEMBRANE. 



organ have an additional and dense covering 

 of areolar tissue on that surface : a covering, 

 which has the same relation to the mucous 

 element, as that on the portal aspect; which is 

 continuous with the capsule of Glisson at nu- 

 merous points; and which is here developed 

 as a membrane of support, as a nidus for a 

 lymphatic rete, and as a foundation for the 

 peritoneal tunic, that it sustains. 



The nerves and lymphatic vessels of the in- 

 terior of the liver, though but little known, are 

 too inconsiderable in point of size to affect the 

 general accuracy of this description. Hence 

 it evidently appears, on what modifications of 

 the elements ot the mucous tissue and of those 

 appended to it, the peculiar friability, colour, 

 and other properties of this organ depend. If 

 the " parenchymatous" areolar tissue abounded 

 in this gland to the extent implied in the de- 

 scriptions of Bichat and some more recent 

 authors, no doubt its toughness would be far 

 greater than it really is. But where an organ 

 is sufficiently screened from injury by its po- 

 sition, where its different parts are so well 

 connected by the continuity of a close network 

 of capillary vessels, and are not required to 

 move on one another, it would be difficult to 

 imagine what purpose a greater development 

 of areolar tissue would serve. 



In the kidney, the epithelial and vascular 

 elements are in corresponding abundance, the 

 areolar tissue in very small quantity. The 

 general texture, however, is more tough than in 

 the liver, from the universal presence of the 

 basement membrane on the tubes. In the me- 

 dullary portion, the tubes radiate from the 

 apex towards the base of the cones, and are 

 imbedded in a firm, granular substance, not 

 hitherto described, but which resembles a 

 blastema, and is probably composed of cells. 

 In this substance is also imbedded the capil- 

 lary plexus surrounding the tubes, as well as 

 the vessels that convey blood to and from this 

 plexus, and take the same direction as the 

 tubes. Hence the firmness and close texture 

 of this part of the kidney as compared with 

 the other, and the facility with which it tears 

 from the apex to the base of the cones. At the 

 base of the cones, the tubes enter the cortical 

 substance and take a course, in sets, towards 

 the surface. The central tubes of each set 

 reach the surface and then recline inwards and 

 become convoluted. But the others bend down 

 one after another and become convoluted before 

 reaching the surface. All at length terminate 

 in the Malpighian bodies, which lie among the 

 convolutions. The arteries and veins also take 

 a general course from the hilus towards the 

 surface. Hence, on tearing the cortical part of 

 the organ, there is a disposition for the lacera- 

 tion to occur in lines continuous with the radii 

 of the medullary cones, and this disposition is 

 less evident as we approach the surface ; but 

 between these lines the torn surface is very 

 uneven, where it is formed by the contorted 

 tubes. The cortical part has less of the inter- 

 tubular matrix than is met with in the medul 

 lary cones. 



In the kidney there is a peculiarity of the 



highest interest in the relative situation of the 

 vascular and mucous tissues, which seems to 

 have reference to the peculiar function of the 

 gland. There are two systems of capillary 

 vessels, the former of which, or that in con- 

 nection with the renal artery, perforates the mu- 

 cous membrane at the extremity of each tube, 

 and lies on the outer surface of the membrane, 

 that is, bare and loose within the dilated ex- 

 tremities, which thus form the capsules of the 

 Malpighian bodies.* (See REN.) 



The common submucous areolar membrane 

 of the kidney, or that forming its capsule, is 

 in most animals chiefly composed of ordinary 

 areolar tissue with close meshes. But where a 

 more resisting covering is required, as in the 

 lion, this areolar tissue is modified ; the white 

 fibrous element predominates so much as to 

 give the capsule the glistening aspect of an 

 aponeurosis. This is an admirable example of 

 the transition from areolar tissue into white 

 fibrous tissue, and helps to show the true nature 

 and relations ofthetunicaalbuginea of the testis. 



The testis, compared with the liver and kid- 

 ney, presents several modifications of the ele- 

 mentary tissues. The basement membrane is 

 much stouter than in the latter gland, the tubes 

 are larger and their convolutions more loosely 

 joined by any intervening substance. There is 

 no appearance of an intertubular substance 

 except towards the corpus Highmorianum, and 

 the principal connecting medium between the 

 tubes seems to be the vessels, which are less nu- 

 merous than in the glands already mentioned, 

 and form a looser network. The secreting tu- 

 bules for these reasons admit of being very 

 easily separated from one another, and un- 

 ravelled to great lengths. The epithelial ele- 

 ment of the testis constitutes a lining of con- 

 siderable thickness, and is highly remarkable 

 (see Jig. 274). Though no seminal animalcules 

 have been hitherto seen in the interior of the 

 particles while still attached to the basement 

 membrane of the tubes, yet from recent re- 

 searches, and especially from those of Wagner, 

 on the phases of their development, it is ren- 

 dered highly probable that these singular 

 moving bodies originate in the epithelial 

 particles, as one of the results of their natural 

 evolution. The loose aggregation of the tu- 

 bules of the testis makes a firm external cap- 

 sule necessary, and where, as in man, this 

 gland is much exposed to injury by its situ- 

 ation, a further protection of this kind is made 

 requisite. Hence the firm and unyielding 

 character of the tunica albuginea in man, 

 the contrast of which with the thin covering of 

 the large but well protected testicle of the por- 

 poise (for example), is well worthy of attention. 

 In many large animals, the tunica albuginea, 

 like the aponeurotic capsule of the lion's kid- 

 ney, is traversed more or less completely by 

 large veins which it thus serves to support. 

 The tunica albuginea consists almost solely of 

 white fibrous tissue, and represents the sub- 

 mucous areolar tissue of the mucous system. 



The peculiarities of the salivary glands re- 



* Phil. Trans. 1842, part I. 



