Licence: Public Domain Mark
Credit: A manual of dissection of the human body / by Luther Holden. Source: Wellcome Collection.
Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.
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![communicating branches descend on the outer side of the internal jugular vein, and form generally two loops in front of the carotid sheath. From these loops the nerves proceed to the depressor muscles of the larynx. In some subjects the descendens noni seems to be wanting ; but look carefully and you wiir probably discover it concealed m^Am the carotid sheath: in such case the reinforcing loops from the cervical nerves will be found behind the internal jugular vein. Let us now examine the thyroid body, and in order to expose it, let us reflect the sterno-hyoid and thyroid muscles from their insertions so that they can be replaced if necessary. Afterwards we will examine the absorbent glands of the neck, and then survey the objects in the central line of the neck, from the jaw to the sternum. This very vascular gland-like substance lies over the boc^°^'^ front and sides of the upper part of the trachea, and ex- tends upwards on each side of the larynx. It consists ot two lateral lobes, connected a little below the cricoid cartilage by a transverse portion called the isthmus. Each lobe is conical, with the base opposite the sixth or seventh ring of the trachea, and the apex by the side of the thyroid cartilage. Its anterior surface is covered by the sterno-hyoid and thjToid muscles; its deep surface clasps the sides of the trachea and larynx, and usually extends so far backwards as to be in contact with the pharynx. Its external border overlaps, in most cases partially, but sometimes completely, the common carotid artery, particularly on the right side ; and there are instances in which the lobe is deeply grooved by the vessel. The isthmus lies over the 2rd, 3rd, and 4th rings of the trachea. This portion of the organ varies much in its dimensions. In some instances there is no transverse portion. This corresponds with the normal disposition in most of the lower orders of mammalia ; but in man it is a failure in the union of the two halves by which the organ is originally deve] oped. Grenerally, the vertical measure- ment of the isthmus is about one inch. Between its upper border and the cricoid cartilage is a space about four or five lines in extent](https://iiif.wellcomecollection.org/image/b21506759_0029.jp2/full/800%2C/0/default.jpg)
