THYROID GLA^ 7 D. 721 



terminate- on the right side in the vena azygos ; on the left side, in the superior 

 intercostal vein. 



The Lymphatics consist of a superficial and deep set ; they terminate at the root 

 of the lung, in the bronchial glands. 



Nerves. The lungs' are supplied from the anterior and posterior pulmonary 

 plexuses, formed chiefly by branches from the sympathetic and pneumogastric. 

 The filaments from these plexuses accompany the bronchial tubes upon which they 

 are lost. Small ganglia have been found by Eemak upon the smaller branches of 

 these nerves. 



THYBOID GLAND. 



The Thyroid Gland bears much resemblance in structure to other glandular 

 organs, and is usually classified together with the thymu% supra-renal glands, and 

 spleen, under the head of ductless glands, from its possessing no excretory duct. 

 Its function is unknown, but, from its situation in connection with the trachea 

 and larynx, is usually described with these, although taking no part in the 

 function of respiration. It is situated at the upper part of the trachea, and 

 consists of two lateral lobes, placed one on each side of this tube, connected 

 together by a narrow transverse portion, the isthmus. 



Its anterior surface is convex, and covered by the Sterno-hyoid, Sterno-thyroid, 

 and Omo-hyoid muscles. 



Its lateral surfaces, also convex, lie in contact with the sheath of the common 

 carotid artery. 



Its posterior surface is concave, and embraces the trachea and larynx. The 

 posterior borders of the gland extend as far back as the lower part of the 

 pharynx. 



This gland is of a brownish-red color. Its weight varies from one to two 

 ounces. It is larger in females than in males, and becomes slightly increased in 

 size during menstruation. It occasionally becomes enormously hypertrophied, con- 

 stituting the disease called bronchocele or goitre. Each lobe is somewhat conical 

 in shape, about two inches in length, and three-quarters of an inch in breadth, the 

 right lobe being rather the larger of the two. 



The isthmus connects the lower third of the two lateral lobes ; it measures about 

 half an inch in breadth, and the same in depth, and usually covers the second and 

 third rings of the trachea. Its situation presents, however, many variations, a 

 point of some importance in the operation of tracheotomy. Sometimes the isthmus 

 is altogether wanting. 



A third lobe, of conical shape, called the pyramid, occasionally arises from the 

 left side of the upper part of the isthmus, or from the left lobe, and ascends as 

 high as the hyoid bone. It is occasionally quite detached, or divided into two 

 parts, or altogether wanting. 



A few muscular bands are occasionally found attached, above, to the body of the 

 hyoid bone, and, below, to the isthmus of the gland, or its pyramidal process ; these 

 were named by Soemmering, the Levator glandulue thyroideve. 



Structure. The thyroid consists of numerous minute closed vesicles, com- 

 posed of a homogeneous membrane, inclosed in a dense capillary plexus, and 

 connected together into imperfect lobules by areolar tissue. These vesicles are 

 spherical or oblong, perfectly distinct, and contain a yellowish fluid, in which 

 are found floating numerous "dotted corpuscles" and cells. The fluid coa- 

 gulates by heat or alcohol, but preserves its transparency. In the foetus 

 and in young subjects, the corpuscles lie in a single layer, in contact with 

 the inner surface of these cavities, and become detached during the process of 

 growth. 



Vessels and Nerves. The arteries supplying the thyroid are the superior and 

 inferior thyroid, and sometimes an additional branch from the arteria innominata, 

 which ascends from this vessel upon the front of the trachea. The arteries are 

 46 



