On the comparative anatomy of the thyroid gland / [John Simon].

  • John Simon
Date:
1844
Catalogue details

Licence: Public Domain Mark

Credit: On the comparative anatomy of the thyroid gland / [John Simon]. Source: Wellcome Collection.

    7/12 page 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), Callorhynchusf', Shark (Squalus), Skate (Raid), and questionably in the Lamprey (Petromyzon). It has appeared, on the other hand, to be absent in the Perch (Perea), Mullet (Mugil), Gurnard (Trigla), Mackerel (Scomber), Tench (Tinea), Salmon (Salrno), 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 anyone of three different positions;— these positions, moreover, related to each other (as would 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.
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