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Show 1890.] HELODERMA SUSPECTUM. 211 There is before me at the present moment a mounted skeleton of a Heloderma suspectum belonging to the U. S. National Museum, wherein the hinder third of the skeleton of the tail has been replaced by feebly developed cartilaginous nodules, and it is very evident that that specimen, in life, sometime or other lost that part of its economy. The Lymphatic system of Heloderma has not been examined by m e; that is beyond what I have given above in reference to the spleen. XII. SOME OBSERVATIONS UPON THE NERVOUS SYSTEM. Although it possesses a peculiar facies of its own, the brain of Heloderma suspectum is quite typically Lacertilian in the majority of its parts. Either olfactory lobe is rather short, comparatively, and is of nearly uniform calibre throughout. The outer envelope of the brain ensheaths these lobes together, up to their anterior tips. Measuring from the posterior surface of the cerebellum to tbe tip of an olfactory lobe, the greatest length of the brain of this reptile is 2§3 centimetres, while is greatest width, taken through the cerebral mass transversely, is one centimetre. Each cerebral hemisphere is reniform in outline, full, and beautifully rounded. The posterior limbs of the somewhat slender optic chiasma are closely applied to the rather large pituitary body, which latter presents the usual infundibulum, and withal has a form much as we find it in Lacerta viridis. Upon opening one of the cerebral hemispheres we observe that the corpus striatum is large and rounded and occupies considerable space in the central cavity. A choroid plexus is easily made out. Turning to the pineal body we find it small and rather inconspicuous, and when the brain is in its case in situ within the skull this structure comes closely in contact on the ventral surface, in the middle line, with a large longitudinal venous sinus that is seen in this cavity in Heloderma. I have made no especial histological examination of the pineal body in our present subject, and consequently cannot with authority say at what stage the "parietal eye" may be: I am of opinion, however, that it is undoubtedly in a very rudimentary condition. It is a fact that a very considerable venous sinus stands between it and the cranial roof, and that not a vestige of a parietal foramen is to be found piercing the latter. This latter feature is well seen in a skull of Lguana tuberculata before me that belongs to the collections of the Smithsonian Institution (No. 12G00). After reading Baldwin Spencer's announcement of his important discovery, it is quite natural that this point should specially interest me upon dissecting the brain of Heloderma \ Young Heloderms show no better development of this eye than do the adult specimens, in so far as I have examined them. Passing to the olfactory lobes, we find them to be rather small in comparison with the size attained by the hemispheres in the Lizard before us, the two lobes together barely having a width equalling the width of one of the hemispheres. 1 Spencer, W . Baldwin, " The Parietal Eye of Hatteria." ' Nature,' May 13th. 1880, p. 33. |
