1884.] 41 fCope. 



evidences of Monotreme affinity observed by Professor Owen and myself 

 in the bones of the legs, especially of the anterior leg. It remains a fact 

 that with this resemblance in the leg there is a general adherence to the 

 reptilian type in the structure of the skull. But this adlierence is not so 

 exclusive as has been supposed, as I will now endeavor to show. 



The structure of the columella auris in Clepstdrops leptoceph- 

 ALUS. — As alreadj' briefly described above, this element is bifurcate at the 

 proximal extremity. The shorter expanded extremity is the stapes proper. 

 The oblique perforation of its base is a character which has not been hitherto 

 observed in any reptile, not even in the allied form Hatteria (Huxley). If, 

 as is probable, the perforation is homologous with the foramen of the 

 mammalian stapes, we have here another point of resemblance to this 

 class. The longer proximal branch of the columella has only half the 

 •width of the stapedial portion, and its long axis makes an obtuse angle 

 ■with that of the latter. It is perhaps the ossified suprastapedial cartilage 

 of Huxley, which that author states (Anatomy of Vertebrated Animals, 

 p. 77) is not ossified in any of the living Sauropsida. Huxley supposes 

 this cartilage to be the homologue of the incus, and remarks * that in a 

 young Mammalian foetus "it appears exactly as if the incus were the 

 proximal end of the cartilage of the first visceral arch." The columella 

 now described resembles a rib, of which the suprastapedial process resem- 

 bles the head, and the stapes the tubercle. If this process be the incus, 

 the stapes is shortened as in the majority of Mammalia, unless the primi- 

 tive suture between the two be longitudinal. The form and position of 

 the true stapes give support to the view of Salensky, that it is not part of 

 a true visceral arch, but is developed in the connective tissue surround- 

 ing the mandibular artery. We see that in this Pelj'cosaurian it is not 

 the proximal part of the arch, and surrounds the mandibular artery. 

 The columella is divided into at least two distinct elements. This is 

 clearly indicated by its abrupt truncation distally by a rough sutu- 

 ral surface. If there is but one bone distad to the stapes, it is homol- 

 ogous witli the cartilage, ■which has been shown by Peters f to be 

 distinct in Hatteria, crocodiles and various lizards. It is the trian- 

 gular ligament of Cuvier. If the suprastapedial be incus, this ele- 

 ment is malleus ; and it is usually identified as such by the older anat- 

 omists. In this structure" we have evidence that the hypothesis that 

 the articular and quadrate bones are homologous with the ossicula auditus 

 is incorrect. The Pelycosauria will probably come under the head of 

 "Sauropsides malleoferes " of Albrecht. We have here an approximation 

 to the Mammalia in two points: (1) The perforation of the head of the 

 stapes ; (2) and the ossification of the incus, which (3) is distinct from the 

 malleus, thus furnishing homologues of the principal ossicles of the ear. It 



♦Proceedings Zool. Society, London, 1869. p. 391. 

 •fMonatsberichte der Academic Sciences, Berlin 1S68 (p. 592)— 1870. 



PROC. AMER. PHILOS. SOC. XXII. 117. F. printed DECEMBER 19, 1884. 



