498 
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 fora 
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 
eral accuracy of this description. Hence 
it evidently appears, on what modifications of 
the elements of 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 thetubes. 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 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 aprerese 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- 
" cones. 
n the kidney there is a peculiarity of the 
MUCOUS MEMBRANE. 
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 membran 
that is, bare and loose within the dilated ex- 
tremities, which thus form the capsules of the 
Malpighian bodies.* (See Ren.) 7 
The common submucous areolar membran 
of the kidney, or that forming its capsule, 1 
in most animals chiefly composed of ordinay 
areolar tissue with close meshes. But where 
more resisting covering is required, as in th 
lion, this areolar tissue is modified ; the whi 
fibrous element predominates so much as 
give the capsule the glistening aspect of a 
aponeurosis. This is an admirable example ¢ 
the transition from areolar tissue into whi 
fibrous tissue, and helps to show the true natui 
and relations of the tunicaalbuginea of the testis 
The testis, compared with the liver and kit 
ney, presents several modifications of the elk 
mentary tissues. The basement membrane 
much stouter than in the latter gland, the tube 
are larger and their convolutions more loose 
joined by any intervening substance. There 
no appearance of an intertubular substant 
except towards the corpus Highmorianum, at 
the principal connecting medium between 
tubes seems to be the vessels, which are less n 
merous than in the glands already men 
and form a looser network. secreting t 
bules for these reasons admit of being ve 
easily separated from one another, and 
ravelled to great lengths. The epithelial e 
ment of the testis constitutes a lining of ec 
siderable thickness, and is highly remarkab 
(see fig. 274). Though no seminal animaleu! 
have been hitherto seen in the interior of 
particles while still attached to the basemen 
membrane of the tubes, yet from recent 
searches, and especially from those of Wagn 
on the phases of their development, it ist 
dered highly probable that these singu 
moving bodies originate in the epithe 
particles, as one of the results of their na 
evolution. The loose aggregation of the 
bules of the testis makes a firm external ¢ 
sule necessary, and where, as in man, t 
gland is much exposed to injury by its : 
ation, a further protection of this kind is 
requisite. Hence the firm unyie 
character of the tunica albuginea in— 
the contrast of which with the thin coveri 
the large but well protected testicle of the 
ise (for example), is well worthy of atte 
n many large animals, the tunica albug 
like the aponeurotic capsule of the lion’: 
ney, is traversed more or less comple 
large veins which it thus serves to su 
The tunica albuginea consists almost sol 
white fibrous tissue, and represents the 
mucous areolar tissue of the mucous syst 
The peculiarities of the salivary glan 
~~ 
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Lic 
ae 
ne 
* Phil. Trans. 1842, part I. 
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