298 MR. SIMON ON THE COMPARATIVE ANATOMY OF THE THYROID GLAND. 
E. Ophidia. 
In the true Serpents the thymus and thyroid are in such close juxtaposition, 
and are in many genera so additionally obscured by the presence of a large fat body, 
that it is not easy to judge, from the vague descriptions of authors, how far the thyroid 
gland itself has actually been discerned. The organ which Blasius* described as a 
thymus “ vasis circa collum situatis accumbens, firmse admodum conditionis, hordei 
magnitudinem vix excedens,” was probably the thyroid gland; Charas^ likewise 
figured it faithfully, though with the same mistake as to its nature. Cuvier had 
certainly dissected it, and describes its exterior conformation with his wonted accuracy, 
stating his impression that it is “analogous to the thyroid gland.” 
The following description applies to all the true Serpents : — The gland lies, as in the 
Crocodile, just above the base of the heart, between the right and left carotid arteries : 
it is a little hidden by the thymus of each side, which lies on the carotid for some 
distance from the pericardium upwards ; and in those genera which possess a fat body 
(as is, for example, eminently the case with the Python) this large organ lies conspi- 
cuously in front of both the thymus and thyroid. 
F. Batraclnia. 
Among Batrachia, Carus^: has recognized the thyroid glands of the common Frog: 
but his statement of their nature appears, like most of the opinions I have quoted, to 
be delivered vaguely and with hesitation. The organs which he represents are un- 
questionably thyroid glands ; they are situated on the carotid arteries, just beside the 
cornua of the hyoid bone, one on each side. Huschke, in adopting Carus’s descrip- 
tion, suggests that these bodies probably have their origin in the shrinking of the 
branchiae, and he proceeds to apply the theory so obtained to the thyroid gland in 
other animals, stating the common mode of origin of this organ to lie in the trans- 
formation of the branchial arches in the early embryo §. But this hypothesis appears 
sufficiently refuted by the anatomy of the Menobranchus lateralis ; for in this peren- 
nibranchiate reptile the thyroid gland exists no less certainly than in those which 
possess the branchial apparatus only for a time. I have found the gland in this animal, 
consisting of two symmetrical portions connected with the inferior border of the os 
hyoides, one on each side, at the junction of the body and lateral portions of that bone. 
In the Menopoma I have likewise detected the gland, occupying nearly the same 
relative position as in the Menobranchus. In the Siren and Proteus I have had no 
opportunity of making satisfactory examinations. 
In the Salamandridse the same arrangement prevails as in the Ranidae. 
In the anomalous Lepidosiren paradoxa the thyroid gland appears also to exist. 
* Anat. Animalium, Amst. 1681 . 
.t Loc. cit. 
f Nouvelles Experiences sur la Vip£re, ch. v. sect. 3. fig-. 2. D. 
§ Oken’s Isis, 1826, p. 621. 
