1102 



THYMUS GLAND. 



thymus. Absence of the gland has only been 

 observed in cases of acephalism, where the 

 brain and many other parts are simultane- 

 ously deficient, while in cases of anence- 

 phalism, where the brain is also wanting 

 wholly, but the general development much 

 more complete, the thymus is present ; no- 

 thing therefore can be concluded from its 

 absence in cases of extreme monstrosity as 

 Mr. Simon has well observed. 



Inflammation of the gland, if it ever happens, 

 is of rare occurrence. Professor Hope, however, 

 refers to a case by Mason, in which an abscess 

 of the thymus is said to have opened into the 

 trachea. 



The same author states that Becher and 

 Hangstadt have collected about fifteen ex- 

 amples of persons, of different ages, affected 

 with more or less general tubercular disease, 

 in whom the thymus was found involved. 

 " It was for the most part considerably en- 

 larged, very firmly united with surrounding 

 parts, and either converted by tubercular in- 

 filtration into a hardened mass, or else par- 

 tially destroyed by tuberculous softening. In 

 three or four instances calcareous concretions, 

 probably resulting from the retrogression of 

 tubercle, were discovered in the gland." 



Haller speaks of the thymus as being fre- 

 quently affected with scirrhus along with the 

 conglobate glands ; but though Becher gives 

 an instance on his own authority, and refers 

 to others, there can be no doubt that true 

 malignant disease of the gland is extremely 

 rare. Sir A. Cooper gives a case, in which 

 death was produced by the pressure of an 

 enlarged thymus upon the vena transversa 

 and upon the trachea, probably also upon the 

 vagi nerves ; there was severe dyspnoea and 

 oedema of the lower extremities. He considers 

 the disease to have been of the fungoid kind, 

 i. e. encephaloid. 



Atrophy of the thymus occurs as a normal 

 event ; if, however, it should take place long 

 before the usual period, determined, as we 

 have seen, not so much by the lapse of time 

 as by the condition of the system, it must be 

 regarded as morbid. Yet in every such case it 

 is almost certain that the atrophy of the thy- 

 mus would be but part of a general malady, 

 wherein the nutrition of every organ was 

 greatly impaired. 



Hypertrophy of the thymus has attracted 

 more attention, Dr. Kopp having noticed 

 several cases of suddenly fatal dyspnoea oc- 

 curring in children, in whom the gland was 

 found of large size, concluded that there was 

 some essential connection between the glan- 

 dular enlargement and the suffbcative pa- 

 roxysms. The fallacy of this opinion has been 

 well pointed out by Mr. Simon and others. I 

 must refer to his work, and that of Professor 

 Hope, for a full account of their arguments, 

 and will only mention two circumstances, 

 which seem to me conclusive upon the point. 

 The first is, that "thymic asthma" may occur 

 with an unnaturally small thymus ; the second, 

 that when a thymus, enlarged by malignant 

 disease, as in Sir A. Cooper's case, does oc- 



casion dyspnoea, it is not sudden and pa- 

 roxysmal, but constant and exhausting. 



For the history of the thymus, and for a copious 

 list of authors who have written upon it, I can do 

 no better than refer to the Historical Introduction to 

 Mr. Simon's essay. 



(C. Handfield Jones.) 



THYROID GLAND. (French, glande 

 thyro'ide ; German, Die Schilddruse ; Italian, 

 Tiroidca glaiidola ; Latin, GlandulatliyroidcEa.} 

 The organ which has received this name is a 

 bilobed glandular body, situated in the human 

 subject in close proximity to the larynx, from 

 the prominent cartilage of which it has pro- 

 bably derived its appellation. 



Its size varies considerably in different in- 

 dividuals, according to unknown peculiarities. 

 In the female it is generally larger than in 

 man ; reversing thus the proportion which 

 obtains between the vocal apparatus in the 

 two sexes, and so far negativing the idea, 

 that the larynx and the thyroid gland are in 

 any wise intimately connected. 



The normal weight of the thyroid is about 

 one ounce, according to Cruveilhier. Any 

 great excess above this must be regarded as 

 indicating a pathological condition. 



Its form, as has been said, is bilobed ; the 

 lateral lobes being united by a thinner and 

 narrower portion termed the isthmus. It 

 would appear (from the circumstance that 

 variations of form are most frequent in the 

 isthmus, which sometimes is even wanting) 

 that the lateral lobes are the primary parts of 

 the gland, and, in fact, in one entire class 

 (that of birds) the lobes lie entirely separate, 

 one on each side of the trachea. In the human 

 subject they are large and solid, presenting an 

 anterior convex surface, a posterior concave, 

 an external and inferior border which is con- 

 vex, and runs up to join the superior interior 

 concave border in a pointed cornu, which 

 reaches as far as the origin of the inferior con- 

 strictor pharyngis from the ala of the thyroid 

 cartilage. From the upper border of the 

 isthmus, or from the adjacent part of one of 

 the lateral lobes, there stretches upwards a 

 narrow strip of glandular tissue, which has 

 been called the pyramid or mesian column, 

 and which may have been sometimes mis- 

 taken for a muscle, as Cruveilhier asserts ; 

 though it is distinguished perfectly from the 

 so called Icvator gland, thyroid, by Haller. 

 This prolongation sometimes extends to the 

 hyoid bone, but generally not so far, and is 

 subject to numerous modifications of shape 

 and structure. The following list of the 

 various forms which the thyroid may pre- 

 sent, is taken from the catalogue of the mu- 

 seum of Guy's Hospital, which Dr. Birkett, the 

 curator, most kindly allowed me to inspect, 

 together with the preparations. 1. Thyroid 

 without an isthmus, but having two mesian 

 columns. 2. Thyroid almost without an 

 isthmus, and having one mesian column. 3. 

 Thyroid with broad isthmus and one mesian 

 column. 4. Thyroid with no isthmus, but 

 having one large mesian column. 5. Thyroid 



