. Anterior jugular vein.

4. Hyoid half of omo-hyoid muscle.

5. Sterno-hyoid muscle.

6. Top of the sternum.

7. Clavicle.

8. Trapezius muscle.

9. Splenius capitis and colli muscle.

10. Occipital half of occipito-frontalis muscle.

11. Levator auris muscle.

12. Frontal half of occipito-frontalis muscle.

13. Orbicularis oculi muscle.

14. Zygomaticus major muscle.

15. Buccinator muscle.

16. Depressor anguli oris muscle.

(Page 16)

[Illustration: Right side of the head, showing blood vessels, muscles
and other internal organs. ]
Plate 4

COMMENTARY ON PLATES 5 & 6.

THE SURGICAL FORM OF THE DEEP CERVICAL AND FACIAL REGIONS, AND
THE RELATIVE POSITION OF THE PRINCIPAL BLOODVESSELS AND
NERVES, &c.

While the human cervix is still extended in surgical position, its
deeper anatomical relations, viewed as a whole, preserve the
quadrilateral form. But as it is necessary to remove the
sterno-cleido-mastoid muscle, in order to expose the entire range of the
greater bloodvessels and nerves, so the diagonal which that muscle
forms, as seen in Plates 3 and 4, disappears, and thus both the cervical
triangles are thrown into one common region. Although, however, the
sterno-mastoid muscle be removed, as seen in Plate 5, still the great
bloodvessels and nerves themselves will be observed to divide the
cervical square diagonally, as they ascend the neck from the
sterno-clavicular articulation to the ear.

The diagonal of every square figure is the junction line of the opposite
triangles which form the square. The cervical square being indicated as
that space which lies within the mastoid process and the top of the
sternum--the symphysis of the lower maxilla and the top of the shoulder,
it will be seen, in Plate 5, that the line which the common carotid and
internal jugular vein occupy in the neck, is the diagonal; and hence the
junction line of the two surgical triangles.

The general course of the common carotid artery and internal jugular
vein is, therefore, obliquely backwards and upwards through the diagonal
of the cervical square, and passing, as it were, from the point of one
angle of the square to that of the opposite--viz., from the
sterno-clavicular junction to the masto-maxillary space; and, taking the
anterior triangle of the cervical square to be that space included
within the points marked H 8 A, Plate 5, it will be seen that the common
carotid artery ranges along the poster