Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Todd, Robert Bentley
maceration, the intervals between the fibres 
become greater, and as the putrefactive pro¬ 
cess sets in and advances, the whole substance 
of the middle tunic takes on the form of a 
spongy mass, and ultimately the fibres cease 
to be any longer discernible, having been re¬ 
duced to the state of a soft pulp, while the 
cellular structure is rendered more evident. 
The following appears to us to be the rationale 
of the phenomena above described : the in¬ 
crease in thickness which the middle tunic at 
first undergoes is owing to the cellular tissue 
interposed between the fibres imbibing the 
water in which it has been immersed, in virtue 
I of its hygrométrie property ; and tbe spongy 
appearance observable after the maceration 
has been continued for a length of time, is the 
result of the cellular tissue having the property 
of resisting decomposition by putrefaction 
much longer than the fibrous tissue. 
The internal tunic (intima of Haller) is the 
thinnest of the three ; it is continuous with 
the lining membrane of the heart, in extending 
from which into the arteries it forms a dupli- 
cature, contributing to the composition of the 
, semilunar valves : in the larger arteries, when 
empty, it sometimes forms longitudinal folds ; 
in some arteries, such as the poplitæal, and the 
brachial at the bend of the elbow, it presents 
transverse folds or wrinkles; it also forms 
transverse wrinkles in arteries which have re- 
• tracted after amputation : its internal surface, 
which is in contact with the blood in the living 
body, is smooth, polished, and bedewed with 
a fine exhalation ; its external surface adheres 
to the internal surface of the middle tunics in 
the larger trunks of the arteries; this tunic 
may be divided into two layers, the internal 
of which is thin and transparent, while the 
external is whitish and opaque, having its struc¬ 
ture blended with that of the middle tunic ; 
it is the tunica cellulosa interior of Haller, 
and is the seat of the calcareous, steatomatous, 
and atheromatous deposits, which so frequently 
occur as morbid appearances in the coats of 
the arteries. We do not perceive fibres nor 
any other signs of organization in the inner 
layer of this tunic in its healthy state; it is 
almost completely inelastic and very brittle; 
it tears with equal facility in every direction ; 
compared with other structures it bears the 
closest resemblance to the arachnoid mem¬ 
brane of the brain; the smooth and highly 
polished condition of the free surface of this 
tunic is an admirable provision, whereby the 
effect of friction in diminishing the velocity 
of the passage of the blood through the arte¬ 
ries is reduced to the smallest possible amount. 
The following mechanical contrivance ob¬ 
servable in the interior of the arteries would 
appear to be a provision for facilitating the 
distribution of the blood through the divisions 
of the arterial system. As the branches of the 
arteries mostly arise from the trunks at acute 
angles, the portion of the circumference of 
their orifices on the side next the heart is 
smooth and depressed, forming a sort of chan¬ 
nel sloping gently from the trunk into the 
branch, while the opposite side, or that more 
remote from the heart, is bordered by a ridge 
of a semilunar valve-like form, composed of a 
duplicature of the lining membrane in which 
there is included a portion of the middle 
tunic ; the more acute the angle at which the 
branch arises, the greater is the prominence of 
this ridge ; it is altogether absent where branches 
arise at right angles, as in the case of the emul- 
gent arteries, and where branches arise at ob¬ 
tuse angles to the trunk, it is found at their 
orifices on the side next the heart. 
The aorta and pulmonary artery are each 
provided with three valves at their origins from 
the ventricles ; these valves, called sigmoid or 
semilunar from their semicircular form, are 
attached by their inferior borders, which are 
convex, to the margins of the semicircular 
flaps or festoons, into which the edge of the 
commencement of the middle tunic of the 
artery is divided ; the superior edges of each 
of these valves, which are free and floating, 
form two concave lines, separated by a 
projection in the centre, in which is con¬ 
tained a small cartilaginous body, called 
tubercle, globulus Arant'd or corpus sesa- 
moideum. The portions of the walls of the 
artery corresponding to the valves are dilated 
in the form of pouches, more marked in the 
aorta than in the pulmonary artery ; these are 
the sinuses of Valsalva. The semilunar valves 
are composed of a duplicature of the lining 
membrane of the artery, including within it a 
thin but strong fibrous expansion, continuous 
with the fibrous structure, which connects the 
middle tunic of the artery with the tendinous 
ring encircling: the arterial opening of the ventri¬ 
cle ; the free border of each valve contains a small 
fibrous cord, as described by Beclard, having 
the globulus Arantii attached to it in its centre. 
An increase or diminution in the number of 
the sigmoid valves is of rare occurrence, more 
frequently presented in the pulmonary artery 
than in the aorta, and oftener consists in the 
number of valves being increased to four than 
diminished to two.* 
The mechanism of these valves is such as to 
prevent the blood flowing in a direction con¬ 
trary to its regular course ; for when that fluid 
is propelled towards the ventricle, they are 
separated from the parietes of the artery, and 
being distended by the column of blood pres¬ 
sing against their superior surfaces, they are 
laid across the area of the vessel, which they 
completely fill up by their edges being thus 
brought into perfect contact and the globuli 
Arantii meeting in the centre. There are no 
valves in the arteries in any other situation. 
The arteries, like other organized struc¬ 
tures, are furnished with proper nutritious 
arteries and veins called vasa vasorum. The 
aorta and pulmonary artery at their commence¬ 
ment receive some branches from the coronary 
vessels of the heart ; in all other situations the 
vasa vasorum are supplied by the neighbouring 
bloodvessels ; the vasa vasorum are very evi¬ 
dent in the external tunic of the arteries, they 
can be traced until they penetrate the sub¬ 
stance of the middle tunic, but not farther ; 
* Meckel, Handbuch der menschlichen Anato¬ 
mie. Band. i.


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