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.

[Illustration: Right side of the head and neck, showing blood vessels,
muscles and other internal organs.]
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 relat