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Show 206 DR. R. W. SHUFELDT O N [Apr. 1, Just at this point I will pass from the consideration of those organs that arc entirely contained either within the body- or mouth-cavities and record next a few brief notes upon some external structures, such, for instance, as the poison-glands and their ducts1. VII. THE POISON-GLANDS. (Plate XVI. fig. 4.) J. G. Fischer (44) has presented us with a fair drawing of the venom-organs oi Heloderma horridum as they occur upon either side of the lower jaw. Of the ducts, of which there are four in the specimen I dissected, they passed, at a short distance apart, from the mesial aspect of the middle of the gland upwards each to its opening on 1 Before parting company, however, with our researches upon the organs contained in the coelom and the cavity of the thorax, I would like to say a word or two more in reference to the observations I have made concerning the system of hepatic, cystic, and pancreatic ducts ; and, secondly, as to the description recorded of the thyroid gland of Heloderma. In the case of the first-mentioned structures I desire to repeat the statement that m y opinion abovit them is not final, as I should very much like to see additional material and fully re-investigate structures that seem to be so notably different from the more usual arrangement of these ducts in other vertebrate forms. To be sure I devoted several hours to the careful examination of the ducts in question, and, as far as the circumstances would admit, I was satisfied in m y own mind as to the peculiarities they presented; but that part of the vascular system of the specimen undergoing dissection was not injected, and this may have given opportunity for error. Notwithstanding the cautionary words I here give, both m y description of these parts and m y drawings of them may be absolutely7 correct; and if they be, why so much the better for the writer and his reputation. Speaking of these hepatic ducts I see that Professor Hoffmann found some interesting arrangement of them in Alligators and Crocodiles (see Bronn's ' Thier-Reichs,' Kept. Bd. vi. 33 & 34 Lief., 1882), and, according to him, the distribution of the ducts varies for different species of Alligators, as shown by the drawings in the work quoted (Taf. C). It must be evident, however, from what I have said upon a former page of this memoir, and from what Beddard found in a species of Varanus with regard to its biliary ducts, that further investigation into these structures in Lizards will well repay the labours of the morphologist. As to the thyroid gland in Heloderma, and the description I have recorded in reference to it, I would say that I a m aware of the position occupied by this structure in other Lizards, as in Lacerta it occurs as two separate lobes opposite each other on the sides of the trachea some little distance above the base of the heart. I examined with no little care the organ I have described as the thyroid in our present subject; it was firm and flexible, and under a lens of moderate power had all of the appearances that characterize glandular tissue. Be it noted, too, that the pericardial sac does not normally extend anteriorly beyond the base of the heart, nor connect witli any other sac overlying the origin of the great vessels that I a m at present aware of. Still, a small rupture had taken place in one of the thin auricles of m y specimen and some blood had escaped into the pericardial sac, and this, stained with its o w n colouring-matter and hardened with the alcohol, had, I must confess, some little resemblance to the structure I have described as the thyroid ; but it may have been a resemblance and nothing more. The parts were all particularly sound and perfect otherwise; furthermore, after carefully dissecting up both sides of the trachea, I utterly failed to find in m y specimen any such thing as a thyroid in the locality wherein it occurs in Lacerta. Again, it may have been some pathological growth, Dut an examination of a few recently killed Heloderms would soon clear up all such doubtful points, and I sincerely trust that some day this will be done. |