THYROID GLAND. 



1103 



without isthmus, having one column (rig/it), 

 and an isolated portion on the left. 6. Thy- 

 roid with one lobe only developed, and a 

 little glandular body below the middle of 

 thyroid cartilage. 7. Thyroid gland replaced 

 by a membranous substance, two small por- 

 tions only remaining. 8. The gland with 

 isthmus and two mesian columns. 



It is important to ascertain accurately the 

 situations and relations of the thyroid. I give 

 them as they are stated by Cruveilhier, ^and 

 confirmed by my own observation. The 

 isthmus lies across the first four rings of the 

 trachea, the first not being completely co- 

 vered.* Its upper margin is about half an inch 

 below the interior border of the cricoid carti- 

 lage : from it the mesian column passes up- 

 ward, lying upon the crico-thyroid muscle, 

 the thyroid cartilage, and the thyro-hyoid 

 membrane. The lower border of the isthmus 

 is free, and occasionally descends so low, that 

 there is not space between it and the sternum 

 to perform the operation of tracheotomy. 

 Posteriorly, the isthmus is firmly attached to 

 the rings of the trachea by close and dense 

 areolar tissue. The sterno-hyoid and sterno- 

 thyroid muscles overlap the greater part of 

 the isthmus ; a small portion, however, in the 

 median line is covered only by deep cervical 

 fascia, and perhaps crossed by some branches 

 of origin or communication of the anterior 

 jugular veins. The lateral lobes, concave 

 posteriorly, embrace, and rest against the sides 

 of, the trachea, the cricoid cartilage, the in- 

 ferior and lateral parts of the thyroid car- 

 tilage, and the lower part of the pharynx 

 and upper part of the oesophagus. " These 

 lobes form, with the connecting isthmus, a 

 half or sometimes three fourths of a canal, 

 which surrounds all these parts. This re- 

 lation, one of great importance, explains 

 how certain goitres flatten the trachea late- 

 rally, hinder deglutition, and finally bring 

 on a real asphyxia from strangulation."f The 

 posterior border of the lateral lobes corre- 

 sponds to the vertebral column, and rests 

 upon the carotid artery ; but, if enlarged, it 

 extends further outward, and lies upon the 

 jugular vein. Both recurrent nerves ascend 

 behind the lateral lobes, and are closely in 

 relation with them as they pass under the 

 lower edge of the inferior constrictor muscle. 

 Anteriorlv, the sterno-and omo-hyoid muscles 

 pass in front of the lateral lobes, the sterno- 

 thyroid is stretched as a thin band over their 

 surface, and in cases of considerable hyper- 

 trophy may be seen sunk in a deep groove 

 formed in their substance, or, as Cruveilhier 

 states, expanded to a width double or treble 

 its natural size. These muscles separate the 

 thyroideal lobes from the sterno-cleido-mas- 

 toid, which, with the mastoid artery and the 

 superficialis descendens on its inner surface, 

 overlaps their greater extent, as it passes 

 backwards and upwards to its cranial attach- 

 ment. " The superior extremity of each of 



* There is probably some variation in this, ac- 

 cording to the varying depth of the isthmus, 

 f Cruveilhier, Anat. Descr. 



the lateral lobes terminating in a point, 

 whence the bicorned form which has been 

 attributed to the thyroid body, corresponds 

 on the inside of the carotid artery to the 

 lateral and posterior part of the thyroid car- 

 tilage, and extends sometimes even to the 

 neighbourhood of its upper border. The 

 inferior extremity, thick and rounded, descends 

 more or less low in different subjects, and 

 corresponds to the fifth, sixth, or even to the 

 seventh ring of the trachea; it is situated 

 between the trachea and the common carotid 

 artery. By the inferior extremity the inferior 

 thyroid artery reaches the gland." " The 

 superior border is concave, and skirted by the 

 superior thyroid arteries." The inferior is 

 convex, and has branches of the inferior 

 thyroid running along it. 



The thyroid gland is of a red or reddish 

 yellow colour, of tolerably firm consistence, 

 and gives to the touch the sensation of 

 granulations. Cruveilhier, thus describing, 

 proceeds as follows : " This organ presents 

 all the anatomical characters of glands, 

 and, like them, is separated by dissection 

 into glandular grains " (doubtless meaning 

 the acini of Malpighi) ; "but there is, be- 

 tween these glandular grains and those of 

 ordinary glands, this difference, that in the 

 thyroid gland the glandular grains communi- 

 cate with each other, while in the others they 

 are independent." He then details the result 

 of mercurial injection, to show that the glan- 

 dular grains, or granulations, have a vesicular 

 structure, and communicate with each other ; 

 this latter statement, however, is certainlv 

 erroneous, as we learn from more accurate 

 modes of investigation. The presence of a 

 certain amount of secreted fluid, in the natural 

 condition of the tissue of the thyroid, and 

 the accumulation of a similar material in 

 larger quantities under certain morbid con- 

 ditions, the eminent French anatomist justly 

 regards as evidence of the thyroid possessing 

 a secreting apparatus ; but, at the same time, 

 faithful to the results of accurate dissection, 

 he acknowledges that no excretory duct can 

 be found leading either into the trachea, the 

 ventricles of the larynx, or the foramen 

 caecum of the tongue, whither earlier ob- 

 servers had, with too nice refinement, sought 

 to trace its course. Far truer and more phy- 

 siological than such straining after uniformity 

 is the conclusion he adopts : " I think that 

 there exist, in the economy, glands without 

 excretory ducts, such as the thymus, the supra- 

 renal capsules, and the thyroid gland. The li- 

 quid produced in the gland is absorbed entirely, 

 and fulfils unknown uses." I have thought it 

 worth while to follow this accurate and trust- 

 worthy anatomist through his account of the 

 structure of the thyroid, though it be some- 

 what antiquated, partly for the sake of the 

 confirmation it affords to the results of a 

 more recondite and powerful analysis, and 

 partly that we may observe how securely we 

 may trust Nature's own teachings, even when 

 they may appear, for a time, contradictory to 

 established doctrines, as doubtless it must 



