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X. On the Comparative Anatomy of the Thyroid Gland. By John Simon, Esq., Assist- 
ant-Surgeon to the King's College Hospital, and Demonstrator of Anatomy in King's 
College. Communicated by Joseph Henry Green, Esq., F.R.S., Senior Surgeon 
to St. Thomas's Hospital, Professor of Anatomy to the Royal Academy, 8$c. &fc. 8$c. 
Received June 11, — Read June 20, 1844. 
Few portions of comparative anatomy appear in a less satisfactory condition than 
that relating' to the organs which have been classed together as glands without ducts. 
Since any attempt to illustrate the obscure physiology of these bodies must of neces- 
sity be founded on a precise knowledge of their distribution in the animal kingdom, 
the deficiency cannot be considered unimportant; and I accordingly venture to hope 
that the following details may not appear devoid of interest to the Royal Society. 
In recent researches I have had occasion to examine how far the presence of a 
thymus gland extends in the scale of organization : in the present paper I confine 
myself to the comparative anatomy of the thyroid body ; and I hope, on some future 
opportunity, to communicate the result of similar investigations in regard of the 
remaining two organs of the class, viz. the spleen and supra-renal capsule. 
In pursuing the present subject, and particularly in that part of it which treats of 
Reptiles, I have been under the greatest obligation to my friend Mr. Gray of the 
British Museum, by whose kindness I have enjoyed opportunities of examining many 
animals which I could not otherwise have procured. I have likewise owed much to 
the liberality of the Council of the Royal College of Surgeons, who have permitted 
me access to their rich assortment of store-preparations. 
The careful dissections of Meckel and Cuvier (as recorded in the former’s 
Abhandlungen aus der menschlichen u. vergleichenden Anatomie u. Physiologic, 
Halle, 1806, and in the latter’s celebrated lectures) leave no question as to the 
universal existence of a thyroid gland in the class of inammiferous animals. It is 
therefore unnecessary to dwell upon this point, and I proceed at once to consider the 
anatomy of the gland in the other classes of Vertebrata. 
I. Birds. 
Some writers on the comparative anatomy of Birds have described “ two glands, 
one on each side of the trachea, very near the lower larynx, and frequently attached 
to the jugular veins; which they regard as the analogues of the thyroid gland*.” 
* Owen in Cyclop, of Anat. vol. i. p. 348 ; Cakus, Vergleich. Anat. § 741. 
MDCCCXLIV. 2 Q 
