VARIATION IN THE SKULL AND HORNS OF THE ISABELLA 



GAZELLE. 



By Gerrit S. Miller, Jr., 



Curator, Division of Mammals, United States National MvLSeum. 



Mr. George L. Harrison, jr., has recently presented to the United 

 States National Museum eight skulls of male Gazella isahella Gray 

 taken during 1911 in a limited area near Jebel Bawati, Nubia. Five 

 are fully adults of essentially uniform age, wdth basal suture obliter- 

 ated, permanent dentition in place, and posterior molar moderately 

 worn. The others, also uniform in age, are considerably younger, 

 with basal suture open, milk dentition present tliough much worn, 

 and third molar not fully in line with other teeth. The individual 

 variations occurring in these specimens seem worthy of special note. 



Skull. — In general proportions the skull does not vary conspicu- 

 ously (see table of measurements, page 172). Premaxillary in con- 

 tact with nasal in five specimens, not in contact in two (lost in the 

 remaining skull). The shape of its upper extremity ranges from 

 broadly, almost spatulately, truncate to narrowly tapering. Nasals 

 varying considerably in length (34-48) and in relative breadth (ratio 

 of breadth to length ranging from 40 to 50), posterior termination of 

 bones usually pointed, but broadly rounded in 173824; deepest 

 point of emargination of anterior border lying distinctly on outer 

 side of middle in four specimens, at middle in three (one broken). 

 Lachrymal pits not noticeably variable in development; vacuit}' at 

 least twice as large in No. 173822 as in No. 173824. On ventral 

 aspect of skull the chief regions of variation are the auditory bullae 

 and the posterior termination of palate. The portion of bulla 

 exposed on ventral surface of skull ranges fi'om 23 by 12 to 27.4 by 17; 

 height above level of basioccipital 4.6 to 6.8, least Avidth of basi- 

 occipital between bullae 13,6 to 17. (In the skull with largest bullae 

 the condylobasal length is 4 mm, less than in that with the smallest.) 

 Posterior border of palate usually \vith median and lateral emargina- 

 tions extending forward to essentially the same level, but in one 

 adult and one 3'oung the median cleft runs forward about 8 mm. 

 beyond the lateral concavities; deepest point of lateral concavities in 

 adults ranging from about level of posterior border of m^ to middle 

 of hinder lobe of same tooth. 



Proceedings U. S. National Museum, Vol. 42— No, 1890, 



171 



