The anatomical position of the parotid, H, Plate 3, and submaxillary glands, W, Plate 4, is so important, that their extirpation, while in a state of disease, will almost unavoidably concern other principal structures. Whether the diseased parotid gland itself or a lymphatic body lying in connexion with it, be the subject of operation, it seldom happens that the temporo-maxillary branch of the external carotid, F, escapes the knife. But an accident, much more liable to occur, and one which produces a great inconvenience afterwards to the subject, is that of dividing the portio-dura nerve, S, Plate 4, at its exit from the stylo-mastoid foramen, the consequence being that almost all the muscles of facial expression become paralyzed. The masseter, L, Plate 3, pterygoid, buccinator, 15, Plate 4, and the facial fibres of the platysma muscles, A O, Plate 3, still, however, preserve their power, as these structures are innervated from a different source. The orbicularis oculi muscle, which is principally supplied by the portio-dura nerve, is paralyzed, though it still retains a partial power of contraction, owing to the anatomical fact that some terminal twigs of the third or motor pair of nerves of the orbit branch into this muscle. The facial artery, V, and the facial vein, U, Plate 4, are in close connexion with the submaxillary gland. Oftentimes they traverse the substance of it. The lingual nerve and artery lie in some part of their course immediately beneath the gland. The former two are generally divided when the gland is excised; the latter two are liable to be wounded in the same operation. DESCRIPTION OF PLATES 3 & 4. PLATE 3. A A A. Subcutaneous platysma myoides muscle, lying on the face, neck, and upper part of chest, and covering the structures contained in the two surgical triangles of the neck. B. Lip of the thyroid cartilage. C. Clavicular attachment of the trapezius muscle. D. Some lymphatic bodies of the post triangle. E. External jugular vein. F. Occipital artery, close to which are seen some branches of the occipitalis minor nerve of the cervical plexus. G. Auricularis magnus nerve of the superficial cervical plexus. H. Parotid gland. I. Temporal artery, with its accompanying vein. K. Zygoma. L. Masseter muscle, crossed by the parotid duct, and some fibres of platysma. M. Facial vein. N. Buccinator muscle. O. Facial artery seen through fibres of platysma. P. Mastoid half of sterno-mastoid muscle. Q. Locality beneath which the commencements of the subclavian and carotid arteries lie. R. Locality of the subclavian artery in the third part of its course. S. Locality of the common carotid artery at its division into internal and external carotids. [Illustration: Right side of the head, showing blood vessels, muscles and other internal organs. ] Plate 3 PLATE 4. A. Subclavian artery passing beneath the clavicle, where it is crossed by some blood-vessels and nerves.