202 DK. R. W. SHUFELDT ON [Apr. 1, 



The Heart and Great Vessels. — Such examination as I gave tliis 

 organ, and the vessels leading to and from it, revealed to me nofliing 

 that might be considered especially remarkable. Upon comparing 

 the entrance and emergence of the principal veins and arteries as they 

 take ))lace 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 Verte- 

 brates ' (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 

 right auricle has nearly double tlie capacity of the left, and the left 

 has nearly three times that of the ventricle. Nothing especial seems 

 to characterize the sinus venosus, sinu-au7'icular aperture, the septum 

 auricularum, or tlie auriculo-ventricular aperture or its valve, or the 

 viusculi 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 im- 

 jiresjion 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 thefront of the larynx represents the fflottideal aperture ; 

 it is unguarded by any epiglottideal valve, but its lips are closely 

 apj)osed to each other, and are thick, being so constructed that food 

 is ])revented from getting into the windpipe. There is a median 

 membranous frsenum 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 Wieders- 

 heini'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 par- 

 ticularly the dorsal surface of the 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-laterally, upon either side, outside the larynx, a 

 cricoidal process. Extending from a cricoidal process to the ante- 

 rior tip of the arytenoid bone of the same side, we have a dilator 

 muscle, which by its contraction will open the glottis. Then, ante- 

 riorly, 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- 



