192 PROF. CLELAND ON THE CLASSIFICATION OF THE VERTEBRA. 



THE AUTHOFiS REPLY. 



April, 1898. 



Permit me to thank the Institute, and especially the members 

 who took part in the discussion, for the kindly reception of my 

 communication . 



With regard to remarks made on the subject of birds and 

 reptiles, I am constrained to mention that the similarity of a 

 tui'tle's skull to a bird's consists mainly in the circumstance that 

 modern turtles and bii'ds are both edentulous. Both have beaks, 

 but in cranial osteology they are widely different. It is true that 

 Huxley used the single occipital condyle as a character to link 

 together the parts of his group sauropsida. But I have pointed 

 out the close relationship of the tvvo-condyled amphibia to the 

 single-condyled reptiles, and it will be readily admitted that the 

 single mesial condyle is produced in a very simple way by con- 

 striction of the basi-occipital bone and fusion of two articular 

 cavities. Curiously, no one till now has attracted attention 

 to the fact that the seal has the two atlanto-occipital articu- 

 lations run into one, and yet is as thoroughly mammalian in its 

 skull as in every other part. The greatest care must be taken 

 not to confuse between homology and analogy. Wings are 

 analogous structures, but those of the pterodactjde, the bird 

 and the bat present totally diffei^ent variations of the skeleton 

 of the pectoral limb, of which they all three are modifications. 

 Homologically a penguin's wings are allied to those of other 

 birds, and are as different as can well be conceived from the fins 

 of a turtle. Questions of this sort are purely anatomical, and 

 those who are familiar with reptilian and avian osteology cannot 

 and do not for a moment admit the possibility of any doubt with 

 regard to them. I have much pleasure in expressing my agree- 

 ment with Dr. Kidd as to the origin of the Monotremata. 



