764 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [18] 



I would also expressly state that the proof just given only applies to 

 the higher fishes, and that every attempt to assume the same condition 

 for the higher organized vertebrate animals also must be premature at 

 least. I would not have mentioned this particularly if attempts had 

 not been made recently to show that the atlas of the Amniota is co-ossi- 

 fied with the cranium in Amphibia. 



Stohr29 first made the interesting discovery that the so-called odon- 

 toid process of the Amphibia is nothing more than the notochord be- 

 coming cartilaginous, and subsequently developing as an ossified pro- 

 cess from the first vertebra. Upon this discovery^" Wiederscheim has 

 made the assertion, for which there is no foundation, that the atlas of the 

 Amniota is to be looked for in the occipital part of the skull of the Am- 

 phibia, and that in consequence of this the first vertebra in these forms 

 corresponds to the axis. 



After considering that the arrangement of the nerves in the occipital 

 region, and of the first spinal nerves in the Selachians and Amphibia, 

 at least in the Urodela, is identical -, that in both, the vagus is the last 

 nerve given off by the brain ; further, that the entire occipital region 

 in the Amphibia appears extraordinarily rudimentary, weighty reasons 

 arose in my mind discrediting the idea that we find in the Amphibia 

 the skull appropriating one of the vertebra, and I rather believed that 

 a complete homology of the skulls in the Amphibia and Selachians must 

 be accepted. Wiederscheim's view has its origin in the one-sided com- 

 parison of the conditions of organization in the Amphibia with that in 

 the Amniota. Existing Amphibia, so far as their crania go, form a very 

 restricted group by themselves, their structure permitting certain com- 

 parisons to be made down the scale toward the Dipnoi and Selachians, 

 but not upward toward the Amniota. Consequently, if one foregoes a 

 direct comparison of the skull of the Amphibia with that of the Am- 

 niota, a phylogenetic interpretation of the ontogenetic facts discovered 

 by Stohr would not be difficult. In all fishes, particularly the Sela- 

 chians, a conically-pointed piece of the chorda extends into the occipi- 

 tal region of the skull, and one need only imagine that this notochord 

 be transformed to cartilage, and afterwards— developed from the first 

 vertebra— to ossify, in order to arrive at exactly the same conditions as 

 they exist in Amphibia. 



Then, to be sure, the odontoid process of the Amphibia is not homolo- 

 gous with the structure bearing the same name in the Amniota, but only 

 presents an analogous formation ; yet the supposition of homology even 

 does not seem to me at all probable, inasmuch as it can be easily shown 



29 Ph. Stohr, History of the Development of the Skulls of Urodela. Zeitschrift f. 

 wise. Zoolog., Bd. 33. 1880. 



30 Wiederscheim, Comparative Anatomy of the Vertebrate Animals, page 60. It is 

 not uninteresting that Albrecht {Zoolog. Anzeiger, 1880, Nos. 64 and 65), upon this 

 same report, draws the opposite conclusion, and interprets the first vertebra of the 

 Amphibia as his imaginary "pro-atlas" lying beyond the atlas, and the odontoid pro- 

 cess of the Amphibia as the basioccipital separated from the cranium. 



