/> divide, in order to expose a deeper organ, has been left holding its

natural level. Thus the order of superposition taken by the integument,

the fasciae, the muscles, bones, veins, nerves, and arteries, which

occupy both the surgical triangles of the neck, will be readily

recognised in the opposite Plates.



The depth of a bloodvessel or other organ from surface will vary for

many reasons, even though the same parts in the natural order of

superposition shall overlie the whole length of the vessel or organ

which we make search for. The principal of those reasons are:--1st, that

the stratified organs themselves vary in thickness at several places;

2d, that the organ or vessel which we seek will itself incline to

surface from deeper levels occupied elsewhere; 3d, that the normal

undulations of surface will vary the depth of the particular vessels,

&c.; and 4th, that the natural mobility of the superimposed parts will

allow them to change place in some measure, and consequently influence

the relative position of the object of search. On this account it is

that the surgical anatomist chooses to give a fixed position to the

subject about to be operated on, in order to reduce the number of these

difficulties as much as possible.



In Plate 7 will be seen the surgical relationship of parts lying in the

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.







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.




















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.