74 MR. L. T. IIOGBKX OX THE 



is evidently within the Xenavthra a tendency fur tlie reduction of 

 the jugal along several genetic lines ; yet despite the variety of 

 structure displayed by the zj'goaiatic arch among Edentata vei'a, 

 there is one feature common to all the families of which it is 

 composed : the jugal, however mnch reduced from behind, not 

 only meets the lacrymal but extends well in front of the orbit 

 though less conspicuously than in the Ungulates. Insignificant 

 as this might at first appear, it is striking in view of the extra- 

 ordinary diversity exliibited in the habit, diet, general 

 organization, and in other characters of the z3'gomatic arch itself ; 

 and there is every reason to i-egard it as a common ancestral 

 peculiarity. 



Whether tliis conclusion is correct or not, tlie Xenarthra are in 

 this respect sharply differentifited from the two spurious groups 

 of Edentata, Pholidota and I'ubulidentata. In the Manid?e the 

 zygomatic arch, being incomplete, superficially resembles that of 

 the Myrmecophagidie ; but there is a zygomatic process to the 

 maxilla and the jugal is absent.. If it were present, it would 

 occupy the middle rather than the anterior portion of the arch as 

 in the Myrmecophagidse. In Oryctero^yus the zygomatic arch is 

 complete ; and the maxilla forms at least half of it, reducing the 

 jugal to a slender rod between it and the well-developed zygo- 

 matic process of the squamosal. It is interesting in relation to 

 Elliot Smith's view* that the Tubulidentata show aflinity with 

 the Protungulate stock, to note that in all modern Ungulates 

 and Hyrax the jugal suffers no displacement on account of the 

 maxilla. 



Among the Carnivora there is striking uniformity in the 

 character of the zygomatic arch which, as Slade observes, main- 

 tains in all outstanding particulai's the same features as those 

 exhibite<l by the Creodonta. It is a robust structure curving 

 upwards generally from behind. The jugal forms a large part of 

 the arch and may extend back to the glenoid as in Lutra : in 

 front, it never extends beyond the anterior boundary of the orbit ; 

 but it articulates with the lacrymal universally in the Fissipedia. 

 On the internal surface of the arch the zygomatic processes of 

 the squamosal and jugal sometimes meet. There is a postorbital 

 process usually on the jugal, and sometiines on the squamosal. 

 The Pinnipedia display the same general characteristics except 

 that the lacrymal is absent. Significantly enough, the jugal 

 extends back to the rim of the glenoid in the two families least 

 specialized to aquatic life — the Otariida- and Trichechidje ; Avhere- 

 as in the true Seals (Phocida?) the extent of the jugal both at its 

 anterior and posterior extremities is in a marked manner more 

 restricted by tiie growth of the maxilla and squamosal, though it 

 cannot truly be sxid that the zygomatic arch is essentially different 

 in other respects. 



* Smith, (i. KUiot. "The Brain in tlie Edentata." Trans. Linn.Soc. London, 

 vii., 1899.— t'/'. also Wortman. "The Gaiiodonta and their relations to the 

 Edentata." Bull. Amcr. Mus. Nat. Hist, ix., 1897. 



