, 7 , n HUMAN ANATOMY. 



PRACTICAL CONSIDERATIONS: THE THYROID BODY 



Congenital absence of the thyroid body, or its atrophy with loss of function, 

 occurring at any time before puberty, is apt to be followed by the interference with nu- 

 triti..n and witli normal mental and physical development that produces the condition 

 kn..un as Actinism. Similar atrophic changes occurring later in life cause y/.*fl?- 

 d.-ma, and tin- same condition also known as cache xia stnnnipnva may be brought 

 alxmt by the complete excision of the gland. Calcification of the gland may take 

 place in old age. The isthmus may be congenitally absent and two separate lobes be 

 present, representing the originally distinct embryonic lateral anlages of the organ. 



tsffty thyroids may undergo hypertrophy and form large masses occupying 

 the pleural or the mediastinal cavity (Osier- Packard) ; or they may develop at the 

 base of the tongue, lingual goitre ; or, on account of their embryonic relation to 

 the thyro-glossal duct (which passes behind the hyoid bone), they may be found in 

 the median line of the neck below or behind the hyoid, and may be mistaken for 

 growths of a different character (page 554). 



The thyroid gland may be temporarily enlarged in women during menstruation. 



Hypertrophy of the thyroid gland (goitre) may be (a) parenchymaious when 

 it results from a general hyperplasia of the gland-tissue; () vascular, due to a 

 great increase in the size and number of the blood-vessels ; (c ) cystic, characterized by 

 the formation of walled-off cavities within the already enlarged gland ; (d ) fibrinous, 

 the connective-tissue elements being in excess ; (<?) exophthalmic (Graves's disease), 

 in which the thyroid enlargement is associated with exophthalmos and functional 

 derangement of the vascular system ; (/) adenomatous \ the hypertrophy affecting 

 one or mon- lobules or the isthmus. This last form appears as a one-sided or asym- 

 metrical swelling, is common, and is often classified with tumors of the thyroid, 

 rarer forms of which arc the cancerous and sarcomatous. It may be noted that the 

 gland is relatively larger in females, and that the right lobe is larger than the left. 

 This has been thought to explain the greater frequency of goitre on the right side, 

 and in women. 



Inflammation of the thyroid is rare, and usually occurs during typhoid or other 

 infections, although it is favored by previous thyroid disease or overgrowth. The 

 tumefaction which it produces may cause acutely many of the symptoms brought on 

 more slowly by the chronic forms of enlargement. These symptoms, so far as they 

 have any anatomiral bearing, are : (i) The swelling rises and falls with the larynx 

 timing d'-glutition. This is due to the attachment of the thyroid gland to the cricoid 

 cartilage by tin- upward prolongations of its capsule known as the suspensory liga- 

 ments and to the subjacent larynx and trachea by connective tissue. (2) Dyspnoea. 

 The gland is covered and its growth anteriorly resisted by the sterno-hyoid and 

 stern o thyroid mu->< -l-s < Fig. 545), and, to a less degree, by the omo-hyoid and the 

 anterior border of the sterno-mastoid. Its forward progress is also resisted by the 

 pretrachcal laver of t In cervical fascia. Its close relation to the trachea, therefore, 

 tender-^ the latter Mibject to direct pressure, especially in the firmer forms of bilateral 

 enlargement, () r in those adenomata which begin in the isthmus or lie between the 

 ILK he.i and the sternum. In the unilateral forms the trachea may be displaced to 

 one sid. //< i, /,/,//,. vertigo^ (\d//t>.^'s, and <-/>is/n.\-is. The relation of the 



outer border of the thvmid to the carotid sheath explains the disturbance of the cir- 

 culation in the carotid and internal jugular (cither through direct pressure or by 

 deflection of the ve^els outward i and accounts for these phenomena. (4) Dys- 

 pha^ia i-, relatively rare, hut may occur as the result of pressure upon the upper 

 end of the gullet or the lower portion of the pharynx. It is more common in left- 

 sided goitiv,, ..wing to tin- ( urvation of the oesophagus towards the left. As a great 



\ the isthmus .it the gland is found between the trachea and oesophagus ( Burns i. 



Ih-phonm, or op lionia, due to pressure upon the recurrent laryngeal nerves. 



/ or hrnit. The.,- may be apparent, and caused by the close relation of 



the enlargement to the common carotid artery, or much more rarely real, and 



duet.) the relativelv enormous Mood supply of the vascular form of goitre, the thyroid 



with its four constant aiteiu > and occasional fifth one (the thyroidea ima, 10 per 



