vicinity of the common carotid artery, at the point of its bifurcation
into external and internal carotids. At this locality, the vessel will
be found, in general, subjacent to the following mentioned structures,
numbered from the superficies to its own level--viz., the common
integument and subcutaneous adipose membrane, which will vary in
thickness in several individuals; next, the platysma myoides muscle, F
L, which is identified with the superficial fascia, investing the outer
surface of the sterno-mastoid muscle; next, the deeper layer of the same
fascia, R S., which passes beneath the sterno-mastoid muscle, but over
the sheath of the vessels; and next, the sheath of the vessels, Q, which
invests them and isolates them from adjacent structures. Though the
vessel lies deeper than the level of the sterno-mastoid muscle at this
locality, yet it is not covered by the muscle in the same manner, as it
is lower down in the neck. At this place, therefore, though the actual
depth of the artery from surface will be the same, whether it be covered
or uncovered by the sterno-mastoid muscle, still we know that the
locality of the vessel relative to the parts actually superimposed will
vary accordingly. This observation will apply to the situation and
relative position of all the other vessels as well. Other occurrences
will vary the relations of the artery in regard to superjacent
structures, though the actual depth of the vessel from surface may be
the same. If the internal jugular vein covers the carotid artery, as it
sometimes does, or if a plexus of veins, gathering from the fore-part of
the neck or face, overlie the vessel, or if a chain of lymphatic bodies
be arranged upon it, as is frequently the case, the knowledge of such
occurrences will guard the judgment against being led into error by the
conventionalities of the descriptive method of anatomists. The normal
relative anatomy of the bloodvessels is taken by anatomists to be the
more frequent disposition of their main trunks and branches, considered
per se, and in connexion with neighbouring parts. But it will be seen by
this avowal that those vessels are liable to many various conditions;
and such is the case, in fact. No anatomist can pronounce with exactness
the precise figure of vessels or other organs while they lie concealed
beneath the surface. An approach to truth is all that the best
experience can boast of. The form and relations of the carotid vessels
of Plate 7 may or may not be the same as those concealed beneath the
same region of Plate 8, at the point R.
The motions of the head upon the neck, or of the neck upon the trunk,
will influence the relative position of the vessels A C B, of Plate 7,
and therefore we take a fixed surgical position, in the expectation of
finding that the carotid artery projects from under the anterior border
of the upper third of the sterno-mastoid muscle, opposite the upper
border of the thyroid cartilage; at this situation of the vessels, viz.,
R, Plate 8, opposite O, the thyroid projection, is in general to be
found the anatomical relation of the vessels as they appear dissected in
Plate 7. Of these vessels, the main trunks are less liable to anomalous
character than the minor branches.
The relative position of the subclavian artery is as liable to be
influenced by the motions of the clavicle on the sternum, as that of the
carotid is by the motions of the lower jaw-bone on the skull, or by the
larynx, in its own motions at the fore-part of the neck. It becomes as
necessary, therefore, in the performance of surgical operations upon the
subclavian artery, to fix the clavicle by depressing it, as in Plate 8,
as it is to give fixity to the lower maxilla and larynx, in the position
of Plate 7, when the carotid is the subject of operation.
The same named structures, but different as to their parts, will be
found to overlie the subclavian artery as are found to conceal the
carotid artery. The skin, the fascia, and platysma muscle, the
sterno-cleido-mastoid muscle, the deep layer of the cervical fascia,
&c., cover both vessels. One additional muscle binds down the subclavian
artery, viz., the scalenus anticus. The omo-hyoid relates to both
vessels, the anterior division to the carotid, the posterior to the
subclavian.
The carotid artery lies uncovered by the sterno-mastoid muscle, opposite
to the upper border of the thyroid cartilage, or the hyoid bone; and the
subclavian artery emerges from under cover of a different part of the
same muscle, opposite the middle of the clavicle. These points of
relationship to the skeletal parts can be ascertained by the touch, in
both instances, even in the undissected body. The thyroid point, O, of
Plate 8, indicates the line, R N, which the carotid artery traverses in
the same figure, along the anterior border of the sterno-mastoid muscle,
as seen in the dissected region of Plate 7. The mid-point of the
clavicle, U, Plate 7, and the top of the sternum in the same figure,
will, while the eye follows the arching line, Z X T V, indicate with
correctness the arching course of the subclavian, such as is represented
in the dissection of that vessel, B, Plate 8.
The subclavian artery has no special sheath, properly so called; but the
deep layer of the cervical fascia, P, Plate 8, which passes under A, the
clavicular portion of the sterno-mastoid muscle, and becomes of
considerable thickness and density, sheaths over the vessel in this
region of its course.
A very complex condition of the veins which join the external jugular at
this part of the course of the subclavian artery is now and then to be
found overlying that vessel. If the hemorrhage consequent upon the
opening of these veins, or that of the external jugular, be so profuse
as to impede the operation of ligaturing the subclavian artery, it may
in some measure be arrested by compressing them against the resisting
parts adjacent, when the operator, feeling for D, the scalenus muscle,
and the first rib to which it is attached, cannot fail to alight upon
the main artery itself, B, Plate 8.
The middle of the shaft of the clavicle is a much safer guide to the
vessel than are the muscles which contribute to form this posterior
triangle of the neck, in which the subclavian vessel is located. The
form or position of the clavicle in the depressed condition of the
shoulder, as seen in Plate 8, is invariable; whereas that of the
trapezius and sterno-mastoid muscles is inconstant, these muscles being
found to stand at unequal intervals from each other in several bodies.
The space between the insertions of both these muscles is indefinite,
and may vary in degrees of width from the whole length of the clavicle
to half an inch; or, as in some instances, leaving no interval whatever.
The position of the omo-hyoid muscle will not be accounted a sure guide
to the locality of the subclavian artery, since, in fact, it varies
considerably as to its relationship with that vessel. The tense cords of
the brachial plexus of nerves, F, Plate 8, which will be found, for the
most part, ranging along the acromial border of the artery, are a much
surer guide to the vessel.
On comparing the subclavian artery, at B, Plate 8, with the common
carotid artery, at A, Plate 7, I believe that the former will be found
to exhibit, on the whole a greater constancy in respect to the
following-mentioned condition--viz., a single main arterial trunk arches
over the first rib to pass beneath the middle of the clavicle, while the
carotid artery opposite the thyroid piece of the larynx is by no means
constantly single as a common carotid trunk. The place of division of
the common carotid is not definite, and, therefore, the precise
situation in the upper two-thirds of the neck, where it may present as a
single main vessel, cannot be predicted with certainty in the
undissected body. There is no other main artery of the body more liable
to variation than that known as external carotid. It is subject to as
many changes of character in respect to the place of its branching from
the common carotid, and also in regard to the number of its own
branches, as any of the lesser arteries of the system. It is but as an
aggregate of the branches of that main arterial trunk which ranges from
the carotid foramen of the temporal bone to the aorta; and, as a branch
of a larger vessel, it is, therefore, liable to spring from various
places of the principal trunk, just as we find to be the case with all
the other minor branches of the larger arteries. Its name, external
carotid, is as unfittingly applied to it, in comparison with the vessel
from which it springs, as the name external subclavian would be if
applied to the thyroid axis of the larger subclavian vessel. The
nomenclature of surgical anatomy does not, however, court a
philosophical inquiry into that propriety of speech which comparative
science demands, nor is it supposed to be necessary in a practical point
of view.
It will, however, sound more euphoneously with reason, and at the same
time, I believe, be found not altogether unrelated to the useful, if,
when such conditions as the "anomalies of form" present themselves, we
can advance an interpretation of the same, in addition to the dry record
of them as isolated facts. Comparative anatomy, which alone can furnish
these interpretations, will therefore prove to be no alien to the
practical, while it may lend explanation to those bizarreries which
impede the way of the anthropotomist. All the anomalies of form, both as
regards the vascular, the muscular, and the osseous systems of the human
body, are analyzed by comparison through the animal series. Numerous
cases are on record of the subclavian artery being found complicated
with supernumerary ribs jutting from the 5th, 6th, or 7th cervical
vertebrae. [Footnote] To these I shall add another, in respect of the
carotid arteries--viz., that I have found them complicated with an
osseous shaft of bone, taking place of the stylo-hyoid ligament, a
condition which obtains permanently in the ruminant and other classes of
mammals.
[Footnote: I have given an explanation of these facts in my work on
Comparative Osteology and the Archetype Skeleton, to which, and also to
Professor Owen's work, entitled Homologies of the Vertebrate Skeleton, I
refer the reader.]
DESCRIPTION OF PLATES 7 & 8.
PLATE 7.
A. Common carotid at its place of division.
B. External carotid.
C. Internal carotid, with the descending branch of the ninth nerve lying
on it.
D. Facial vein entering the internal jugular vein.
E. Sterno-mastoid muscle, covered by
F. Part of the platysma muscle.
G. External jugular vein.
H. Parotid gland, sheathed over by the cervical fascia.
I. Facial vein and artery seen beneath the facial fibres of the platysma.
K. Submaxillary salivary gland.
L. Upper part of the platysma muscle cut.
M. Cervical fascia cut.
N. Sterno-hyoid muscle.
O. Omo-hyoid muscle.
P. Sterno-thyroid muscle.
Q. Fascia proper of the vessels.
R. Layer of the cervical fascia beneath the sterno-mastoid muscle.
S. Portion of the same fascia.
T. External jugular vein injected beneath the skin.
U. Clavicle at the mid-point, where the subclavian artery passes
beneath it.
V. Locality of the subclavian artery in the third part of its course.
W. Prominence of the trapezius muscle.
X. Prominence of the clavicular portion of the sterno-cleido-mastoid
muscle.
Y. Place indicating the interval between the clavicular and sternal
insertions of sterno-cleido-mastoid muscle.
Z. Projection of the sternal portion of the sterno-cleido-mastoid
muscle.
[Illustration: Right side of the head and neck, showing blood vessels,
muscles and other internal organs.]
Plate 7
PLATE 8.
A. Clavicular attachment of the sterno-mastoid muscle lying over the
internal jugular vein, &c.
B. Subclavian artery in the third part of its course.
C. Vein formed by the union of external jugular, scapular, and other
veins.
D. Scalenus anticus muscle stretching over the artery, and separating it
from the internal jugular vein.
E. Post-half of omo-hyoid muscle.
F. Inner branches of the brachial plexus of nerves.
G. Clavicular portion of trapezius muscle.
H. Transversalis colli artery.
I. Layer of the cervical fascia, which invests the sterno-mastoid and
trapezius muscles.
K. Lymphatic bodies lying between two layers of the cervical fascia.
L. Descending superficial branches of the cervical plexus of nerves.
M. External jugular vein seen under the fascia which invests the
sterno-mastoid muscle.
N. Platysma muscle cut on the body of sterno-mastoid muscle.
O. Projection of the thyroid cartilage.
P. Layer of the cervical fascia lying beneath the clavicular portion of
the sterno-mastoid muscle.
Q. Layer of the cervical fascia continued from the last over the
subclavian artery and brachial plexus of nerves.
[Illustration: Right side of the head and neck, showing blood vessels,
muscles and other internal organs.]
Plate 8
COMMENTARY ON PLATES 9 & 10.
THE SURGICAL DISSECTION OF THE STERNO-CLAVICULAR OR TRACHEAL
REGION, AND THE RELATIVE POSITION OF ITS MAIN BLOODVESSELS,
NERVES, &c.
The law of symmetry governs the development of all structures which
compose the human body; and all organized beings throughout the animal
kingdom are produced in obedience to this law. The general median line
of the human body is characterized as the point of fusion of the two
sides; and all structures or organs which range this common centre are
either symmetrically azygos, or symmetrically duplex. The azygos organ
presents as a symmetrical unity, and the duplex organ as a symmetrical
duality. The surgical anatomist takes a studious observation of this law
of symmetry; and knowing it to be one of general and almost
unexceptional occurrence, he practises according to its manifestation.
The vascular as well as the osseous skeleton displays the law of
symmetry; but while the osseous system offers no exception to this law,
the vascular system offers one which, in a surgical point of view, is of
considerable importance--namely, that behind the right sterno-clavicular
articulation, C, Plate 9, is found the artery, A, named innominate, this
being the common trunk of the right common carotid and subclavian
vessels; while on the left side, behind the left sterno-clavicular
junction, Q, Plate 10, the two vessels (subclavian, B, and carotid, A,)
spring separately from the aortic arch. This fact of asymmetrical
arrangement in the arterial trunks at the fore part of the root of the
neck is not, however, of invariable occurrence; on the contrary,
numerous instances are observed where the arteries in question, on the
right side as well as the left, arise separately from the aorta; and
thus Nature reverts to the original condition of perfect symmetry as
governing the development of even the vascular skeleton. And not
unfrequently, as if to invite us to the inquiry whether a separate
origin of the four vessels (subclavian and carotid) from the aorta, or a
double innominate condition of the vessels, were the original form with
Nature, we find her also presenting this latter arrangement of them. An
innominate or common aortic origin may happen for the carotid and
subclavian arteries of the left side, as well as the right. Hence,
therefore, while experience may arm the judgment with a general rule,
such generality should not render us unmindful of the possible
exception.
When, as in Plate 9, A, the innominate artery rises to a level with C,
the right sterno-clavicular junction, and when at this place it
bifurcates, having on its left side, D, the trachea, and on its right
side, B, the root of the internal jugular vein, together with a, the
vagus nerve, the arterial vessel is said to be of normal character, and
holding a normal position relative to adjacent organs. When, as in Plate
10, A, the common carotid, and B, the subclavian artery, rise separately
from the aortic arch to a level with Q, the left sterno-clavicular
articulation, the vessels having M, the trachea, to their inner side,
and C D, the junction of the internal jugular and subclavian veins, to
their outer side, with b, the left vagus nerve, between them, then the
arterial vessels are accounted as being of normal character, and as
holding a normal relative position. Every exception to this condition of
A, Plate 9, or to that of A B, Plate 10, is said to be abnormal or
peculiar, and merely because the disposition of the vessels, as seen in
Plates 9 and 10, is taken to be general or of more frequent occurrence.
Now, though it is not my present purpose to burden this subject of
regional anatomy with any lengthy inquiry into the comparative meaning
of the facts, why a common innominate trunk should occur on the right of
the median line, while separate arterial trunks for the carotid and
subclavian arteries should spring from the aorta on the left of this
mid-line, thus making a remarkable exception to the rule of symmetry
which characterizes all the arterial vessels elsewhere, still I cannot
but regard this exceptional fact of asymmetry as in itself expressing a
question by no means foreign to the interests of the practical.
In the abstract or general survey of all those peculiarities of length
to which the innominate artery, A, Plate 9, is subject, I here lay it
down as a proposition, that they occur as graduated phases of the
bicleavage of this innominate trunk from the level of A, to the aortic
arch, in which latter phasis the aorta gives a separate origin to the
carotid and subclavian vessels of the right side as well as the left. On
the other hand, I observe that the peculiarities to the normal separate
condition of A and B, the carotid and subclavian arteries of Plate 10,
display, in the relationary aggregate, a phasial gradation of A and B
joining into a common trunk union, in which state we then find the aorta
giving origin to a right and left innominate artery. Between these two
forms of development--viz., that where the four vessels spring
separately from the aortic arch, and that where two innominate or
brachio-cephalic arteries arise from the same--may be read all the sum
of variation to which these vessels are liable. It is true that there
are some states of these vessels which cannot be said to be naturally
embraced in the above generalization; but though I doubt not that these
might be encompassed in a higher generalization; still, for all
practical ends, the lesser general rule is all-sufficient.
In many instances, the innominate artery, A, Plate 9, is of such
extraordinary length, that it rises considerably (for an inch, or even
more) above the level of C, the sternal end of the clavicle. In other
cases, the innominate artery bifurcates soon after it leaves the first
part of the aortic arch; and between these extremes as to length, the
vessel varies infinitesimally.
The innominate artery lies closer behind the right sterno-clavicular
junction than the left carotid or subclavian arteries lie in relation to
the left sterno-clavicular articulation; and this difference of depth
between the vessel of the right side and those of the left is mainly
owing to the form and direction of the aortic arch from which they take
origin. The aortic arch ranges, not alone transversely, but also from
before backward, and to the left side of the dorsal spine; and
consequently, as the innominate artery, A, Plate 9, springs from the
first or fore part of the aorta, while the left carotid and subclavian
arteries arise from the second and deeper part of its arch, the vessels
of both sides rising into the neck perpendicularly from the root in the
thorax, will still, in the cervical region, manifest a considerable
difference as to antero-posterior depth. The depth of the left
subclavian artery, B, Plate 10, from cervical surface, is even greater
than that of the left common carotid, A, Plate 10, and this latter, at
its root in the aortic arch, is deeper than the innominate artery. Both
common carotids, A A, Plates 9 and 10, hold nearly the same
antero-posterior depth on either side of the trachea, M, Plate 10, and
D, Plate 9. Although the relative depth of the arterial vessels on both
sides of the trachea is different, still they are covered by an equal
number of identical structures, taking the same order of superposition.
On either side of the episternal cervical pit, which, even in the
undissected body of male or female, infant or adult, is always a
well-marked surgical feature, may be readily recognised the converging
sternal attachments of the sterno-mastoid muscles, L G, Plate 10; and
midway between these symmetrical muscular prominences in the neck, but
holding a deeper level than them, is situated that part of the trachea
which is generally the subject of the operation of tracheotomy. The
relative anatomy of the trachea, M, Plate 10, D, Plate 9, at this
situation requires therefore to be carefully considered. The trachea is
said to incline rather to the right side of the median line; but perhaps
this observation would be more true to nature if it were accompanied by
the remark, that this seeming inclination to the right side is owing to
the fact, that the innominate artery, A, Plate 9, lies obliquely over
its fore part, near the sternum. However this may be, it certainly will
be the safer step in the operation to regard the median position of the
trachea as fixed, than to encroach upon the locality of the carotid
vessels; and to make the incision longitudinally and exactly through the
median line, while the neck is extended backwards, and the chin made to
correspond with the line of incision. And when the operator takes into
consideration the situation of the vessel A, Plate 9, and A, Plate 10,
at this region of the neck, he will at once own to the necessity of
opening the trachea, D, Plate 9, M, Plate 10, at a situation nearer the
larynx than the point marked in the figures. The course taken by the
common carotid arteries is, in respect to the trachea, divergent from
below upwards; and as these vessels will consequently be found to stand
wider apart at the level of K, I, Plate 10, than they do at the level of
M, Plate 10, so the farther upwards from the sternum we choose the point
at which to open the trachea, the less likely are we to endanger the
great arterial vessels.
In addition to the fact, that the carotid arteries at an inch above the
sternum lie nearer the median line than they do higher up in the neck,
it should always be remembered, that the trachea itself is situated much
deeper at the point M, Plate 10, D, Plate 9, than it is opposite the
points F and K of the same figures. The laryngo-tracheal line is, in the
lateral view of the neck, downwards and backwards, and therefore it will
be found always at a considerable depth from cervical surface, as it
passes behind the first bone of the sternum, midway between both
sterno-mastoid muscles.
In the operation of tracheotomy, the cutting instrument divides the
following named structures as they lie beneath the common integument: If
the incision be made directly upon the median line, the muscles F,
sterno-hyoid, and E, sterno-thyroid, Plate 9, are not necessarily
divided, as these structures and their fellows hold a somewhat lateral
position opposite to each other. Beneath these muscles and above them,
thus encasing them, the cervical fascia, f f, Plate 10, is required to
be divided, in order to expose the trachea. Beneath f f the cervical
fascia, will next be felt the rounded bilobed mass of the thyroid body,
lying on the forepart of the trachea; above the thyroid body, the
cricoid and some tracheal cartilaginous rings will be felt; and since
the thyroid body varies much as to bulk in several individuals of the
same and different sexes, as also from a consideration that its
substance is traversed by large arterial and venous vessels, it will be
therefore preferable to open the trachea above it, than through it or
below it.
On the forepart of the tracheal median line, either superficial to, or
deeper than, the cervical fascia, the tracheotomist occasionally meets
with a chain of lymphatic glands or a plexus of veins, which latter,
when divided, will trammel the operation by the copious haemorrhage
which all veins at this region of the neck are prone to supply, owing to
their direct communication with the main venous trunks of the heart; and
not unfrequently the inferior thyroid artery overlies the trachea at the
point D, Plate 9, when this thyroid vessel arises directly from the arch
of the aorta, between the roots of the innominate and left common
carotid, or when it springs from the innominate itself. The inferior
thyroid vein, sometimes single and sometimes double, overlies the
trachea at the point D, Plate 9, when this vein opens into the left
innominate venous trunk, as this latter crosses over the root of the
main arteries springing from the aorta.
Laryngotomy is, anatomically considered, a far less dangerous operation
than tracheotomy, for the above-named reasons; and the former should
always be preferred when particular circumstances do not render the
latter operation absolutely necessary. In addition to the fact, that the
carotid arteries lie farther apart from each other and from the median
place--viz., the crico-thyroid interval, which is the seat of
laryngotomy--than they do lower down on either side of the trachea, it
should also be noticed that the tracheal tube being more moveable than
the larynx, is hence more liable to swerve from the cutting instrument,
and implicate the vessels. Tracheotomy on the infant is a far more
anxious proceeding than the same operation performed on the adult;
because the trachea in the infant's body lies more closely within the
embrace of the carotid arteries, is less in diameter, shorter, and more
mobile than in the adult body.