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.
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.