47 



ON THE HOMOLOGY OF THE PALATIXE PllOCESS 

 or THE MAMMALIAN PR EM AXILLARY. 



By R. Broom, M.B., CM., B.Sc. 



In typical mammals the premaxillaiy l^one may be divided into 

 two more or less well marked parts. There is the anterior and 

 outer part ]3earing the incisor teeth and forming the outer wall 

 and floor of the na,sal cavity at its anterior part, and there is 

 generally an elongated delicate process of bone passing backwards 

 into the palatine region — the palatine process of the premaxillary. 

 Throughout the Mammalia the tooth-bearing part of the pre- 

 maxillary varies comparatively little; but in the palatine process 

 even in closely allied forms we have the most striking variations. 

 Among Marsupials, for example, in the genus Trlcliosiorus the 

 palatine process is exceedingly long, while in the closely allied 

 Phascolarctus it is only slightly developed. 



Opinion seems to be considerably divided as to whether the 

 premaxillary is a single structure, or whether it is in reality 

 composed of two distinct elements. Albrecht,* Suttonf, and 

 Parker I have shown that the palatine process may be distinct in 

 origin from the body of the premaxillary through becoming early 

 united with it, and Howes.^ states as the result of a special 



* P. Albrecht, " Sar la Feute niaxiilaire double sousmuqueuse et les 4 os 

 intermaxillaires de r Ornithoihynque adulte normale." (Briixelles, 1883). 



P. Albrecht, " Die morphol. Bedeutung4e»' seitlichen Kieferspalte, &c." 

 Zooi. Anzeiger, 1879. 



t .1. B. Sutton, " Observations on the Parasphenoid, the Vomer and the 

 Palato-pterygoid Arcade." Proc. Zool. Soo. 1884, p. 566 



t W. K. Parker. " On the Structure and Development of the Skull in 

 the Mammalia," Pt, ii. Edentata ; Pt. iii. Insectivora. Phil. Trans. Koy. 

 Sue. Lond. 1885. 



§ G. B. Howes, " On the Probable Existence of a Jacobson's Organ among 

 the Crocodilja, &c." Proc. Zool. 8oc. 1891. 



