I. Occipital artery crossing the internal carotid artery and jugular vein.
K. Internal jugular vein crossed by some branches of the cervical plexus, which join the descendens noni nerve.
L. Spinal accessory nerve, which pierces the sterno-mastoid muscle, to be distributed to it and the trapezius.
M. Cervical plexus of nerves giving off the phrenic nerve to descend the neck on the outer side of the internal jugular vein and over the scalenus muscle.
N. Vagus nerve between the carotid artery and internal jugular vein.
O. Ninth or hypoglossal nerve distributed to the muscles of the tongue.
P P. Branches of the brachial plexus of nerves.
Q. Subclavian artery in connexion with the brachial plexus of nerves.
R R. Post scapular artery passing through the brachial plexus.
S. Transversalis humeri artery.
T. Transversalis colli artery.
U. Union of the post scapular and external jugular veins, which enter the subclavian vein by a common trunk.
V. Post-half of the omo-hyoid muscle.
W. Part of the subclavian vein seen above the clavicle.
X. Scalenus muscle separating the subclavian artery from vein.
Y. Clavicle.
Z. Trapezius muscle.
1. Sternal origin of sterno-mastoid muscle of left side.
2. Clavicular origin of sterno-mastoid muscle of right side turned down.
3. Scalenus posticus muscle.
4. Splenius muscle.
5. Mastoid insertion of sterno-mastoid muscle.
6. Internal maxillary artery passing behind the neck of lower jaw-bone.
7. Parotid duct.
8. Genio-hyoid muscle.
9. Mylo-hyoid muscle, cut and turned aside.
10. Superior thyroid artery.
11. Anterior half of omo-hyoid muscle.
12. Sterno-hyoid muscle, cut.
13. Sterno-thyroid muscle, cut.
Plate 5
PLATE 6.
A. Root of the common carotid artery.
B. Subclavian artery at its origin.
C. Trachea.
D. Thyroid axis of the subclavian artery.
E. Vagus nerve crossing the origin of subclavian artery.
F. Subclavian artery at the third division of its arch.
G. Post scapular branch of the subclavian artery.
H. Transversalis humeri branch of subclavian artery.
I. Transversalis colli branch of subclavian artery.
K. Posterior belly of omo-hyoid muscle, cut.
L. Median nerve branch of brachial plexus.
M. Musculo-spiral branch of same plexus.
N. Anterior scalenus muscle.
O. Cervical plexus giving off the phrenic nerve, which takes tributary branches from brachial plexus of nerves.
P. Upper part of internal jugular vein.
Q. Upper part of internal carotid artery.
R. Superior cervical ganglion of sympathetic nerve.
S. Vagus nerve lying external to sympathetic nerve, and giving off t its laryngeal branch.
T. Superior thyroid artery.
U. Lingual artery separated by hyo-glossus muscle from
V. Lingual or ninth cerebral nerve.
W. Sublingual salivary gland.
X. Genio-hyoid muscle.
Y. Mylo-hyoid muscle, cut and turned aside.
Z. Thyroid cartilage.
1. Upper part of sterno-hyoid muscle.
2. Upper part of omo-hyoid muscle.
3. Inferior constrictor of pharynx.
4. Cricoid cartilage.
5. Crico-thyroid muscle.
6. Thyroid body.
7. Inferior thyroid artery of thyroid axis.
8. Sternal tendon of sterno-mastoid muscle, turned down.
9. Clavicular portion of sterno-mastoid muscle, turned down.
10. Clavicle.
11. Trapezius muscle.
12. Scalenus posticus muscle.
13. Rectus capitis anticus major muscle.
14. Stylo-hyoid muscle, turned aside.
15. Temporal artery.
16. Internal maxillary artery.
17. Inferior dental branch of fifth pair of cerebral nerves.
18. Gustatory branch of fifth pair of nerves.
19. External pterygoid muscle.
20. Internal pterygoid muscle.
21. Temporal muscle cut to show the deep temporal branches of fifth pair of nerves.
22. Zygomatic arch.
23. Buccinator muscle, with buccal nerve and parotid duct.
24. Masseter muscle cut on the lower maxilla.
25. Middle constrictor of pharynx.
(Page 20)
Plate 6
COMMENTARY ON PLATES 7 & 8.
THE SURGICAL DISSECTION OF THE SUBCLAVIAN AND CAROTID REGIONS, THE RELATIVE ANATOMY OF THEIR CONTENTS.
A perfect knowledge of the relative anatomy of any of the surgical regions of the body must include an acquaintance with the superposition of parts contained in each region, as well as the plane relationship of organs which hold the same level in each layer or anatomical stratum. The dissections in Plates 7 and 8 exhibit both these modes of relation. A portion of each of those superficial layers, which it was necessary to 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.