A SECOND INSTANCE OF THE DEVELOPMENT OF 

 RODENT-LIKE INCISORS IN AN ARTIODACTYL. 



By Gerrit S. M11J.ER, Jr. 



Curator of the Division of MammaU, Umied States Xutioiial Muscion. 



The rodent-like incisors of the extinct Balearic Island goat, Myo- 

 tragus balearicus Bate/ have been regarded as the onlj- instance of 

 the development of such teeth by an even-toed ungulate. " The 

 peculiar character of the incisors [of Myotragus'] * * *," writes 

 Dr. C. W. Andrews,- "has no parallel among the Artiodactyle un- 

 gulates, and the steps by which it has been acquired can only be 

 surmised." Although this appears to be the generally accepted opin- 

 ion on the subject, teeth whose structure nearly approaches that 

 present in the incisors of Myotragus occur in a well-known living 

 artiodactyl, the vicunia; and through the unusual conditions seen 

 in these recent teeth the probable history of the still more specialized 

 dentition of the fossil Balearic goat may be traced. 



Photographs of incisors of Vicugna^ and La^na are reproduced 

 in the accompanying plate; those of Vicugna are at tlie left, and 

 in each instance the upper three figures represent milk teeth. The 

 characters are so \Q.vy obvious that they scarcely require anj^ detailed 

 comment. In Lama the general outline of the tooth in both adult 

 and young is strongly cuneate with the greatest width ranging froni 

 about one-fifth to about one-fourth the greatest length. The root 

 tapers rapidly to a closed base ; the enamel on the lingual side of the 

 crown extends from the distal extremity at least one-third of the 

 distance to the base. The milk (figs. 10-12) and permanent (figs. 



' Geol. Magazine, per. 5, vol. •;, p. 385. September. 1909. 



- A description of the Skull and Skeleton of a Peculiarly Modified Rupicaprine Antelope 

 (Myotragus ialearicus. Bate), with a notice of a New Varietj', M. ieleariciis var. major. 

 Pliilos. Trans. Roy. Soc. Loudon, ser. V>, vol. 206, pp. 281-o03, pis. 19-22. June 30, 

 1915. 



= Gray, Cat. Rum. Mamm. Brit. Mus., p. 101, 1872, type Camehts vicugna Molina. 

 Under the provisions of the International Code the availability of this name does not 

 appear to be interfered with by the existence of the earlier Vicunia Rafinesque (Analyse 

 de la Nature, p. 55, 1814), proposed as a substitute for Lama Cuvier. The peculiarities 

 of the incisors are so great that I would separate the vicunia generically from the 

 llama and guanaco. 



No. 2545 — Proceedings U. S. National r/iustuw. Vol. 63, Art, 



949SG— 24 



