296 MR. SIMON ON THE COMPARATIVE ANATOMY OF THE THYROID GLAND. 
They were first, I believe, mentioned by Perrault*, and were afterwards described 
in several genera of Birds by Ballanti^- and Uttini. Various later observers have 
since noticed these bodies; some considering them as thyroid glands; while others, 
among whom are Meckel, Cuvier and Haugsted, entertain a different opinion of 
their nature. 
In all such uncertainties the microscope is the only conclusive test. By repeated 
and careful examinations, I have satisfied myself that the ultimate structure of these 
doubtful organs is identical with that of the thyroid gland in Mammalia. They con- 
sist, namely, of a dense aggregation of closed vesicles, whereof each is constituted by 
a delicate homogeneous membrane, is invested by a close capillary net-work, and 
contains in its interior either floating cytoblasts, or mature cells, corresponding to 
those of the true glands. 
My dissections of Birds have included all the orders, and, in most instances, several 
families from each : I have never failed to find the thyroid gland, or to recognise its 
peculiar structure : I accordingly presume that it is universally present in this class 
of animals. 
Of its relative position it is unnecessary to say much more than is included in the 
notices of previous observers, and I will merely mention that its relation to the larynx 
seems neither essential nor constant. A more uniform and more important relation 
is included in the fact, that the gland always corresponds to a particular spot of the 
vascular system ; namely, that it lies on the cervical vessels, and receives its supply 
of blood just opposite to the point at which the vertebral and carotid arteries diverge 
to their respective destinations. 
II. Reptiles. 
It is unaccountable that in this class of animals, where the thyroid gland is univer- 
sally manifest, it should have been so generally overlooked. Where noticed, it has 
been, with rare and partial exceptions, either mistaken for the thymus, or confounded 
with it in a common description. 
A. Chelonia. 
Bojanus, in his excellent monograph on the freshwater Tortoise;}:, figures with 
perfect fidelity the body, which I shall directly mention as the thyroid gland ; but he 
does so under the erroneous impression that it is a thymus, and describes it by this 
name: Carus§ likewise falls into the same error as to its true nature. 
* Description de six Otardes, Mem. de l’Acad. t. iii. part 2. p. 319. 
t Ballanti states an opinion of their use which has received pretty general sanction : — “ quod vocis organo 
famuletur glandula hujusmodi in animantibus, id videtur satis comprobare ejus sedes, qu«e nunquam non est 
cum eo organo conjuncta;” and Uttini, who continued his researches, specifies this function more exactly, as 
being “ ad vocales chordas opportune emolliendas et humectandas.” Comment. Bonon. 1783; De Organo Vocis. 
{ Anat. testudinis Europ. figs. 66, 156, 173. § Op. cit. § 740. 
