STRUCTURE OF THE COLUMELLA AURIS IN THE PELYCOSAURIA. 5 



and then turns towards the base of the skull. I trace it directly to a foramen on the superior edge 

 of the sphenoid. It is clearly the facial portion of the seventh nerve (tensor tyinpani), as described 

 by Fischer and Stannius,* and has nothing to do with the auricular bones and cartilages. The 

 only connection, then, with inferior arches which I can detect in this species is the fibrous one with 

 the mandible, and I am doubtful of the significance of this. 



It does not seem practicable to recognize the suprastapedial in the epicoluinella of Clepsydrops 

 ItptocephalusA It would require an excessive shortening of the columella, which might readily be 

 the condition of things in Clepsydrops. But it would require that the suprastapedial should be 

 ossified, and separated by suture from the remainder of the cartilage. Until some form is found 

 in which this cartilage is segmented such a hypothesis has no foundation. The homology of the 

 epicolumella with the incus is, on the other hand, almost certain; first, by the evident propriety 

 of the exclusion of the stapes from the question, on account of its position, and by the history 

 of its origin as shown by Salensky; second, on account of its position relative to both the stapes 

 and the malleus. This being the case, the result follows that the doctrine of Peters that the quad- 

 rate bone is not the incus, as was maintained by Reichert, is the true one.f 



Eeol 



Ecol 



Si 



V. . ^ 



EXPLANATION OF PLATE. 



Fio. 1. Columella amis of Clepsydrops leptooephalus ; internal side. Fig. l<r, external side; 16. proximal extremity; 

 le, distal extremity ; st., bead of stapes; Ecol., epicolumella; d, distal articular surface, especially represented in Fig. 

 lc; e r, foramina of stapedial canal. All figures aie half natural size, excepting le, which is natural size. — From the 

 proceedings of the American Philosophical Society, 1884, p. 46. 



Fig. 2. Auricular bones and cartilages and adjacent parts of Heloderma suspcctum Cope,§ twice natural size. Bo., 

 basioccipital bone ; Exo., exoccipital ; f?., quadrate ; Mn., mandible; Ft., pterygoid ; M. Ft., internal pterygoid muscle ; 

 VII, seventh nerve; Col., columella auris; Hst., hypostapedial process of auricular cartilage; Sst., suprastapedial 

 process; Est., epistapellial process; HI., hypostapedial ligament; EL, epistapedial ligament. 



* Zoiitomie der Fische, p. 154. 



tSuch a hypothesis is suggested after inspection of Huxley's figure of these parts in Hatteria, in Anatomy of 

 Vertebrated Animals, p. 77, Fig. A. See also American Naturalist, 1884, p. 1253; Proceeds. Amer. Philosoph. Soe., 

 1884, p. 41. 



iSee Proceedings Amer. Philosoph. Society, 1884, p. 41, where Peter's view is maintained. 



§ I owe the specimen dissected to my friend Horatio N. Rust, who obtained it on the Gila River, Arizona. 



