83 
ANATOMY. 
very thin near the apex of the heart, and 
very thick towards the basis. 
Lach ventricle is composed of its proper 
distinct fibres; but the left ventricle has 
many more than the right, its substance 
being considerably thicker. Where the two 
ventricles are joined, they form an impervi- 
ous septum which belongs equally to both. 
Opposite to this septum a groove is seen on 
the outside of the heart, one running longi- 
tudinally on the upper, the other on the un- 
der surface: in these grooves the great 
branches of the coronary arteries and veins 
are lodged. 
There is this likewise peculiar to the left 
ventricle, that the fibres which form the in- 
nermost septum of its concave side, form the 
outermost stratum of the whole convex side 
of the heart, which consequently is common 
to both ventricles : so that by carefully un- 
ravelling all the fibres of the heart, we find 
it to be made up of two bags contained in a 
third. 
The anterior or right ventricle is some- 
what larger than the posterior or left, as well 
observed by the ancients, and clearly de- 
monstrated by Mr. Iielvetius. 
The left is a little longer than the right, 
and in some subjects they end exteriorly in 
a kind of double apex. But it appears from 
experiments, that the inequality between the 
parts or the right and those of the left side of 
the heart, is not so great during life as after 
death; for in the hearts of animals killed by 
cutting across the vessels of the neck, and in 
those of persons who have died in battle from 
a wound in the vena cava, or pulmonary ar- 
tery, the inequality is less than we commonly 
perceive. This was first observed by M. 
\ ienssens, professor of anatomy at Altorf. 
Sabatier has made several experiments on 
animals, the result of which is nearly the same 
wit'n that mentioned above. 
All the fibres are not directed the same 
way, though they are all more or less oblique : 
for some end toward the right hand, others 
toward the left, some forward, some back- 
ward, and others in the intermediate places ; 
so that in unravelling them, we find that they 
cross each other gradually, sometimes accord- 
ing to tire length of the heart, and sometimes 
according to its breadth. 
The tubes which cross each other trans- 
versely, are much more numerous than those 
which cross longitudinally : which ought to 
be taken notice of, that we may rectify the 
false notions that .have been entertained con- 
cerning the motion of the heart ; namely, 
that it is performed by a contortion or twist- 
ing like that of a screw, or that the heart is 
shortened in the time of contraction, and 
lengthened in dilation. 
The fibres which .compose the inner or 
concave surface of the ventricles do not all 
reach to the basis ; some of them running 
into the cavity and there forming the fleshy 
columns to which the loose floating portion 
of the tricuspidal valves is tastened by tendi- 
nous cords. 
Besides these fleshy pillars the internal 
fibres form a great many eminences and de- 
pressions, which not only render the inner 
surface of the ventricles uneven, but give it a 
great extent within a small compass. Some 
of these depressions are the orifices of the 
vena! ducts, found in the substance of the 
ventricles, which have been already mention- 
ed. 'The circumference of the great open- 
ings of the basis of the hei.rt are tendinous, 
and may be looked upon as the common 
tendon of all the fleshy fibres, of which the 
ventricles are composed. 
Valves. The valves at tire orifices of the 
ventricles are of two kinds; one kind allows 
the blood to enter the heart, and hinders it 
from going out the same way ; the other kind 
allows the blood to go cut of the heart, but 
hinders it from returning. r l lie valves of the 
first kind terminate the auricles ; and those 
of the second lie in the openings of the great 
arteries. The first are termed semilunar or 
sigmoid valves; the others tricuspidal or mitral. 
The tricuspidal valve of the right ventricle 
is of a circular form, and is fixed to the open- 
ing of the auricle, while the other end is 
attached to the internal surface of the ven- 
tricle. The circular membrane of the valve 
soon divides into many parts, three of which 
are more considerable than the rest ; and 
those have got the name of tricuspid valves, 
though they are now generally considered as 
forming one. That which is next the month 
of the pulmonary artery is the largest, and 
is said by some to prevent the blood from 
getting into the artery, while the ventricle is 
filling. It has three triangular productions, 
very smooth and polished, on that side which 
is turned towards the auricle ; and on the side 
next the cavity of the ventricle, they have 
several membranous and tendinous expan- 
sions, and their edges are notched or indent- 
ed. The valve of the auricular orifice of the 
left ventricle is of the same shape and struc- 
ture, but it is only divided into two parts ; 
and, from some small resemblance to a mitre, 
has been named mitralis. That which is 
next the mouth of the aorta is the largest. 
The semilunar valves are six in number, 
three belonging to each ventricle, situated 
at the mouths of the great arteries, and they 
may be properly enough named valvulae ar- 
teriales. Their concave sides are turned to- 
ward the cavity of the arteries, and their 
convex sides approach each other. In ex- 
amining them with a microscope, v r e find 
fleshy fibres lying in the duplicature of the 
membranes or which they are composed. 
They are truly semilunar, or in form of a 
crescent 'on that side by which they adhere ; 
but their loose edges are of a different figure, 
each of them representing two small cres- 
cents ; the two extremities of which meet at 
tiie middle of this edge, and there form a kind 
of small papilla, first described by Arantius, 
and afterwards bv Morgani, and therefore 
named from them. 
The great artery that goes out from 
the left ventricle is termed aorta. At the 
beginning of the aorta, and behind the semi- 
lunar valves, three elevations are observed on 
the outside: these correspond to an equal 
number of pits on the inside, which from the 
discoverer have been called sinuses of Val- 
solva. Their use is not well known. 
The trunk of the artery which goes out 
from the right ventricle is called arteria pul- 
monaris. T his trunk, as it is naturally situ- 
ated in the thorax, runs first of all directly 
upward for a small space, then divides later- 
ally into two principal branches, one for each 
lung; that which goes to the right lung being 
the longest, for a reason that shall be given 
hereafter. 
Auricles. The auricles are muscular bags 
situated at the basis of the heart, and their 
capacities are in proportion to those of their 
respective ventricles ; one toward the right 
ventricle, the other toward the left, and 
joined together by an inner septum, and ex- 
ternal communicating fibres, much in the 
same manner with the ventricles ; one of 
them being named the right auricle, the other j 
the left. Ihey are very uneven on the in- j 
side, but smoother on ihe outside, and ter- 
minate in a narrow, fiat, indented edge, re- 
presenting a cock’s comb, or in some measure j 
the ear ot a dog ; this properly gets the name 
of auricle, the larger and smooth part of the 
cavity being called sinus venosus ; but as the 
two parts make one general cavity, the name 
of auricle is commonly applied to the whole. 
They open into the orifices of each ven- 
tricle, which 1 name auricular orifices ; and 
they are tendinous at their openings, in the 
same manner as the ventricles. 
The right auricle is larger than the left, 
and joins the right ventricie by a common 
tendinous opening, as has been already ob- 
served. It has two other openings united 
into one, and formed by two large veins 
which meet and terminate there almost in a t 
direct line, called vena cava, superior and 
inferior. Highmore has described an eminence 
in form of a valve, placed between the mouths 
of the two venae cava; : this he supposed directs 
the blood from the veins into the auricle ; afo 
terwards Lower described and delineated it ; 
and other anatomists have called it tuber-- 
eulum Loweri, till Morgagni denied its ex- 
istence in the human subject. At the mouth 
of the inferior cava, we find a membrane in 
form of a crescent, described by Lustuchius, 
and named from him. Its convex edge is 
fixed to the union of the vein and right au- 
ricle, while its concave edge is turned up- 
ward over the mouth of the vein. It is most 
complete in the foetus ; but it is found like 
wise in a person of advanced age, though it 
sometimes from use lias a reticular appear- 
ance. It is said to prevent the blood in the; 
auricle from returning into the cava ; but it 
has a different use in the foetus.. The notch- 
ed edge of this auricle terminates obliquely 
in a kind of obtuse point, which is a small 
particular production of the great bag, and i 
turned toward the middle ot the basis of the 
heart. 
The whole inner surface of the right au-j 
ride is uneven, by reason of a great number] 
of prominent lines which run across the side 
of it, and communicate with each other 
smaller lines which lie obliquely in the intes-j 
tines between the former, 'i he lines of the [ 
first kind represent trunks, and the other 
small branches run in an opposite direction to 
each other : these are called musculi pectinat* 
In the interstices between these lines the sides! 
of the auricle 
are very thin and almost! 
transparent, seeming to be formed merely 
by the external and internal coats of the au-j 
{ ride joined together, especially near the 
j point. 
j The left auricle is in the human body a 
1 kind of muscular bag or reservoir of a pretty! 
j considerable thickness, and unequally square, 
! into which the four veins open called veiuej 
j pulmonarcs, and which has a distinct ap- 
i pendix belonging to it like a third small au- 
1 ride. This bag is very even on botli sur- 
I faces, and is therefore called sinus venosus ; j 
J but to distinguish it from the one on tliej 
