[Footnote: I have given an explanation of these facts in my work on Comparative Osteology and the Archetype Skeleton, to which, and also to Professor Owen's work, entitled Homologies of the Vertebrate Skeleton, I refer the reader.] 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. [Illustration: Right side of the head and neck, showing blood vessels, muscles and other internal organs.] Plate 7 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. [Illustration: Right side of the head and neck, showing blood vessels, muscles and other internal organs.] Plate 8 COMMENTARY ON PLATES 9 & 10.