1890.] HELODERMA SUSPECTUM. 209 



insertions as seen in the Lizards generally, the following muscles 

 were examined, viz : — 



122. Rectus anterior. 



123. Rectus posterior. 



124. Rectus superior. 



125. Rectus inferior. 



126. Obliquus superior. 



127. Obliquus inferior. 



128. Musculus choanoides. 



129. Pyramidalis. 



130. Levator palpebrcB superioris. 



131. Depressor palpebrcB inferioris (feebly developed). 



132. Orbicularis palpebrarum (feebly developed). 



The pupil is round, and the sclerotal plates are thin, these latter 

 having each a form somewhat similar to what we find in Birds. 

 Careful examination failed to demonstrate the presence of the pecten 

 within the eyeball, though future specimens may go to show its 

 presence. It is known to be absent in Hatteria and Chelonia^. 

 Around the entrance of the optic nerve the sclerotic coat seems to 

 occasionally slightly ossify. I have also found this to be the case 

 in a variety of genera of 13irds. We find the cornea to be not very 

 markedly convex, while the lens is comparatively of good size, it 

 being quite flat externally, and convex upon its internal aspect. 



X. Notes on the Anatomy of the Ear. 



Heloderma has the tympanum of the ear large and fully developed, 

 making the usual attachments to the parts and bones in the 

 vicinity, thus creating a capacious meatus. Upon dividing this, the 

 external ear-drum, all around at its periphery, and reflecting it, we 

 bring into view the cartilagino-osseous chain of elements that connect 

 the tympanum with the inner ear. Both the passage of the 

 Eustachian tube and the cavity of the middle ear are capacious. 

 Lying along the dorsal roof of this chamber, and close to it, we 

 observe the well-developed columella auris ; it passes forwards and 

 inwards and very slightly upwards ; the osseous rod-like portion 

 being included in a fold of the common lining epithelium, as is like- 

 wise the iufra-stapedial process in its own fold. 



The middle ear is partially divided into two cavities by the inner 

 edge of the quadrate bone, and we see that it is within the inner part 

 of this cavity that the ossified medio-stapedial portion of the colu- 

 mella auris lies, while the outer cartilaginous extremity of the rod 



^ Since writing the above I have carefully examined an eye in very fair con- 

 dition from an alcoholic specimen oi Heloderma suspecfiim, and in it I discovered 

 an extremely delicate fold of tissue extending from the capsule of the leus to a 

 point near the entrance of the optic nerve. It was non-pigmented. This 

 structure quite possibly represents the pecien or "falciform process," but it is 

 here by no means so well marked as I iiave found it in many species of Birds. 



Of course the demonstration of the presence of a tapetivm in old alcoholic 

 specimens of Helodenna is difficult, and I was not successful in any instance. 



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