MR. SIMON ON THE COMPARATIVE ANATOMY OF THE THYROID GLAND. 299 
Bischoff, in his elaborate dissection of that animal*, discovered a minute glandular 
organ, adjoining the anterior extremity of each isolated cornu of the os hyoides, and 
inclined to consider it as a salivary gland. I have had no opportunity of examining 
this rare reptile, but Bischoff’s account is so complete and circumstantial as almost 
to supply the absence of personal observation. The minute body in question cannot be 
viewed as a salivary gland, for it is expressly stated by Bischoff to be destitute of an 
excretory duct. This last point almost decides its true place in the animal economy ; 
and further, its position, in regard to the hyoid bone, is so exactly that occupied by 
the thyroid gland in the Menopoma and Menobranchus, that (from Bischoff’s de- 
scription) I cannot hesitate in ascribing to it the same nature. 
III. Fishes. 
I am not aware that any author has hitherto suggested the possible existence of a 
thyroid gland amongst this class of vertebrate animals. 
In many fishes it is undoubtedly present ; I have found it in the Carp ( Cyprinus ), 
Anableps'f'-, Pike (. Esox ), Exocetus-f, Cod ( Gadus ), Haddock {Morrhua), Whiting 
{Merlangus), Eel {Anguilla), Sturgeon {Acipenser), Callorhynchus f, Shark (, Squalus ), 
Skate {Raia), and questionably in the Lamprey {Petromyzon ) . 
It has appeared, on the other hand, to be absent in the Perch {Perea), Mullet 
{Mugil), Gurnard (2 rigid), Mackerel {Scomber), Tench {Tinea), Salmon {Salmo), 
Trout [Salmo fario), Herring {Clupea), Plaice {Pleuronectes), Holibut {Hippoglossus ) , 
Turbot {Rhombus), Sole {Solea), Cyclopterus, Gymnotus and Balistes-}'. 
This part of my inquiry has been attended with extreme difficulty. According to 
varying circumstances the gland may occupy any one of three different, positions ; — 
these positions, moreover, related to each other (as w r ould appear at first sight) by no 
very obvious analogy. It was long after discovering a thyroid gland in the Skate, 
and vainly searching for it in the corresponding region of the body in other fishes, 
that a second probable spot occurred to me, in which I succeeded in finding the 
gland in the Cod, Haddock and Whiting; and it was yet longer before I ascertained 
the organ’s third occasional site. Such having been the case, it has of course been 
no easy matter to arrive at trustworthy results as to the absence or presence of the 
gland in each particular instance. In forming the negative conclusion, there was 
always some fear of having overlooked the organ, — always some doubt of its occupy- 
ing an unexplored space. The positive certainty, which alone is valuable in investi- 
gations of this nature, cannot often be derived from examining preparations preserved 
in spirit; and, therefore, although I have made many such dissections, I refer to 
* Lepidos. Parad. anatomisch untersucht und beschrieben, Leipzig, 1840. 
f In those marked by a dagger, I have been obliged to trust to preparations preserved in spirit ; and these 
dissections — especially with a negative result — are never quite so satisfactory as if performed on the recent 
body of the animal. 
