MAMMALS OF THE MEXICAN BOUNDARY. 



225 



processes of the frontal bone of the skull, which consist of simple 

 flattened blades (fig. 33) of the bone, called horn cores, covered by a 

 horny sheath having a decurvecl tip and flattened lateral prong. The 

 prong-horn antelope differs from the true antelopes in the deciduous 

 character of the horny sheaths of the horn cores. Avhich are fre- 

 quently, perhaps annually, shed. The horny sheath is a result of a 

 special development of the outer skin or epidermal tissue covering the 

 horn cores. In males the end of the horn is whitish horn color, all 

 of the remainder glossy black ; but in the female the horns are all 

 black. An adult male (No. 440, Mearns's collection), killed August '2, 

 1886, in the Mogollon Mountains of central Arizona, had horns which 

 Avere loosened and nearly 

 ready to be shed. With 

 some difficulty I managed 

 to pull them off, and 

 found new horn sheaths 

 growing beneath. They 

 Avere still in the condition 

 of vascular, hirsute mem- 

 branes of considerable 

 thickness, resembling or- 

 dinary integument, and 

 coated rather sparsely 

 with long hairs. At the 

 apex was a soft, fleshy, 

 nip})le-like process, loose 

 and without hair, Avhich 

 first becomes converted 

 into horn, forming the 

 whitish tips. The apices 

 of these bony tips w'ere 



o/.r. 'i. 1 1 Fig. 33.— SKri.i- of Axtilocapra ameeicana mexicana. 



2()0 mm. apart, and each 



measured 175 mm. in length, from the hair of the forehead. The 

 horns themselves measured as follows: Total length, following the 

 curves, 380 mm.; length, in a straight line from recurved tip to 

 base, 245; from base to superior base of the prong, 148; length of 

 ])rong, 60; width of prong at base, 55; circumference of horn near 

 base, 150; circumference of horn above prong, 104. The horns 

 are much compressed laterally from the base to the prong, which 

 latter is remarkably flattened; above the prong the horn becomes 

 subcylindrical. In this individual the horns w^ould probaldy have 

 been cast before the middle of September. An adult male (No. 

 276, Mearns's collection), killed near the same locality, in the pine 

 forest of the Mogollon Mountains, November 4, 1885, had recently 

 cast the horn sheaths; those replacing them were thickly coated 

 30639— No. 56—07 m 15 



