Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol. 3: Ins-Pla
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit29464/183/
175 
NORMAL ANATOMY OF THE LIVER. 
of the organ is, however, more apparent than 
real, for the numerous cells may be considered 
as so many follicles from which smaller fol¬ 
licles are developed. The cellular character of 
the organ depends upon the more extensive 
subdivision of the follicles, their assemblage 
in greater numbers, their consequent compres¬ 
sion, and the adhesion of their parietes. In 
the Sepia family the spongy structure of the 
hepatic organ is still more distinct. It is chan¬ 
nelled into numerous canals, from which smaller 
canals branch off in various directions; from 
these branches cells are developed, and the 
arietes of the cells are every where surrounded 
y smaller and smaller cells, the entire texture 
being very similar in arrangement to the cel¬ 
lular lung of the higher reptilia. 
The liver in Vertebrata is more close and 
complex in its structure and less amenable to 
the observations of the anatomist than in the 
inferior series. We observe nothing, even in 
the lowest fishes, which bears any direct com¬ 
parison with the cellular structure of the liver 
of Cephalopoda. The general character of the 
organ in fishes is loose and flabby, shewing 
that, although difficult to demonstrate, its in¬ 
ternal texture evidently contains numerous tu- 
buli. If the efferent duct of the liver of a 
fish be inflated, the whole organ appears dis¬ 
tended ; hence we might infer that the primi¬ 
tive structure of the organ is precisely the 
same, consisting in the ramifications of the 
hepatic tubuli or ducts, the increased wants 
and higher position of the animal demanding 
an augmented extension of surface. This is 
the great principle in the development of all 
glandular organs—extension of surface. The 
simple follicle is sufficient for an animal so low 
in the scale as a cavitary entozoon, but as the 
functions of the animal increase, its simple fol¬ 
licle must be extended to a greater length, or 
branched or ramified ; and as high in the ani¬ 
mal scale as the Vertebrata these subdivisions 
have attained so great a degree of minuteness 
that they are demonstrable to the practised eye 
only through the aid of the highest microscopic 
powers. 
Miiller arranges the glandular system into 
simple and compound glands. The former he 
divides into two groups : 1. “ simplest glands,” 
which “ are mere recesses of greater or less 
dimension in the surface of a membrane ;” and 
2. “ more complicated forms/’ in which se¬ 
veral of the recesses are assembled together 
and open by so many distinct mouths, or they 
unite and form a common duct which termi¬ 
nates by a single opening. The “ compound 
glands” he likewise subdivides into two groups: 
1. those which “ ramify with a certain degree 
of regularity, the principal trunk giving off 
branches laterally at certain intervals, these 
sending out in the same way side branches, 
which in their turn afford a third set.” This 
disposition constitutes lobulated glands, and is 
the type of conformation of the liver in Inver- 
tebrata. 2. “ The second group of the glands 
with ramified secreting tubes consists of those 
in which the ramification is irregular, and in 
which there is no division and subdivision of 
the gland into” secreting “ lobules. The liver 
of Mammalia belongs to this group.” 
The form of the liver in Fishes corresponds 
with the direction of the long axis of the body ; 
thus, for instance, it is elongated, and con¬ 
sists of a single lobe in the eel, while in the 
skate it is broad and extends into each lateral 
half of the abdominal cavity. In other fishes 
it is variously divided into lobes, and is often 
placed altogether on the left side of the body. 
In the class Amphibia, the liver also corresponds 
with the form of the body of the animal : in the 
frog it is short and divided into two primary lobes 
and several lobules; in the lengthened forms it 
is long and less divided. In the class Reptilia 
the liver is large, and bears an equal relation to 
the form of the visceral cavity. It is long and 
undivided in Ophidia, and short and divided 
into a right and a left lobe in Sauria and Che- 
lonia, the two lobes being spread out over the 
intestines. In Birds there is great uniformity 
in the form and size of the liver. It is smaller 
in proportion to the bulk of the body than in 
Reptilia and Fishes, and larger than in Mam¬ 
malia. It is situated in the middle line of the 
visceral cavity, and receives the heart into a 
depression upon its under surface. In the 
class Mammalia the liver is very much reduced 
in size, and is more compact and firm than in 
the lower vertebrata. In animals with simple 
stomachs it is situated in the middle line of the 
abdomen. In others, with large or compound 
stomachs, it is pressed towards the right side. 
The number of lobes does not depend upon a 
greater or less division of the liver into parts 
in accordance with the activity and mobility of 
the animal, but obeys a law in the animal 
economy, by which new parts are superadded 
in proportion to the increase of the wants of 
the creature. Man is placed at the foot of the 
scale in the progressive complication in exter¬ 
nal form of the liver of vertebrata ; the entire 
organ may be considered in him as a central 
lobe, the lobus Spigelii being the rudiment of 
a second or right lobe. The liver of the ourang 
offers the same character. Ruminants have 
also a liver which presents the most rudimen¬ 
tary form of division. The liver of man is the 
type of the central or principal lobe, to which 
are added upon each side, in the animal scale, 
a right and a left lobe, and from these latter 
are developed a right lobule and a left lobule. 
This most complicated form of liver, consisting 
of five lobes, is met with among Carnivora and 
Rodentia; and throughout Mammalia, the suc¬ 
cessive additions and subtractions from this 
normal type form a constant and generic cha¬ 
racter. Besides this real division of the liver 
into five lobes, fissures of various depth are 
constantly met with, as in man, which give 
the appearance of a much greater subdivision. 
These secondary portions are to be looked upon 
as the mere results of separation, and have no 
relation with the primitive type. A most ex¬ 
traordinary form of liver is met with in a small 
rodent animal from Cuba, the Capromys, in 
which the whole surface is divided by deep 
fissures into small masses of a triangular and 
quadrangular form, like the kidney of a bear.
        

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