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Show 202 DR. R. W. SHUFELDT ON [Apr. 1, The Heart and Great Vessels.-Such examination as I gave this organ, and the vessels leading to and from it, revealed to m e nothing that might be considered especially remarkable. Upon comparing the entrance and emergence of the principal veins and arteries as they take place from the cardiac cavities in the lizard before us, I find that the arrangement agrees rather with Lacerta than it does with Varanus. In making this assertion I am obliged to rely largely upon the two figures given in the ' Comparative Anatomy of Vertebrates' (p. 285, fig. 229, A & B), where the arrangement of the vessels is seen to be very different in these two types of Lizards. With respect to the heart, the walls of the atria are markedly thin in Heloderma, while, on the other hand, the ventricular parietes are composed of thick muscle of a spongy nature, which renders the single cavity of that division of the heart especially small. The ri°mt auricle has nearly double the capacity of the left, and the left has nearly three times that of the ventricle. Nothing especial seems to characterize the sinus venosus, sinu-auricular aperture, the septum auricularum, or the auriculo-ventricular aperture or its valve, or the musculi pectinati, all of which structures I examined with great care. Such notes as may seem to be required hereafter upon the general venous and arterial systems will be given, but it is my present impression they are not distinguished from the same, as we find them in ordinary Lizards, by any marked peculiarity. Of the Lungs and Air-passages.-The larynx is seen to be placed dorsad to the base of the tongue, riding above it, as it were, while the deep-black integumental mucous membrane which lines the buccal cavity ensheaths them both. A sharp, thin, medio-vertical slit occurring on the front of the larynx represents the glottidealaperture ; it is unguarded by any epiglottideal valve, but its lips are closely apposed to each other, and are thick, being so constructed that food is prevented from getting into the windpipe. There is a median membranous fraenum connecting the anterior end of the tracheal tube to the base of the tongue, but beyond lying immediately over the hyoidean apparatus, the larynx seems to bear no special relation to the last-named structure. I mention this fact, for the reason that Professor W . N. Parker has said (in his translation of Wiedersheim's work), in speaking of the larynx of reptiles, " One point, however, must be specially noticed, viz., the close connection which obtains between the larynx and the hyoidean apparatus-more particularly the dorsal surface of tbe basi-hyal" (loc. cit. p. 255). The structure of the larynx in Heloderma is quite simple: we have at its summit, upon either side, a movably articulated arytenoid bone, and postero-laterallv, upon either side, outside the larynx, a cricoidal process. Extending from a cricoidal process to the anterior tip of the arytenoid bone of the same side, we have a dilator muscle, which by its contraction will open the glottis. Then, anteriorly, in the median line, dorsad, we find the larynx is roundly notched : a constrictor muscle arises from the base of this notch, one for either side, and passing round outside the larynx, becomes in- |