SKELETON OF QUADRUMANA. 527 



no outward indication, but are extensive ; they are divided from 

 each other by a median bony septum ; each division communi- 

 cates mth the nasal chamber by a median orifice and by a lateral 

 one with the antrum. The nasals, 15, join above with the frontals 

 and at the sides with the premaxillaries, 22. The presphenoid is 

 short, smooth on the under surface, and concave there trans- 

 versely. The vomer quickly assumes the form of a vertical plate, 

 with the free hind border concave. The palatines form the 

 hinder third of the bony palate ; the suture of each with the 

 maxillary is slightly convex forward : they are divided from the 

 inner alveolar wall of the last two molars by a groove which 

 deepens into a fissure, bounded beyond the last molar by the 

 pterygoid. The maxillary forms more than the middle third of 

 the palate, leaving the smallest share of the roof of the mouth to 

 the premaxillary. The facial plate of the maxillary, 21, extends by 

 a narrow produced apex to the lacrymal, 73, but is excluded from 

 the frontal by the junction of the lacrymal with the premaxillary ; 

 it is perforated by a small antorbital foramen. The premaxillaries 

 constitute a larger share of the facial wall, rising as high as the 

 nasals, between which and the maxillaries they interpose a broad 

 plate, circumscribing, with the nasals, the external nostril. The 

 socket of the incisor curves upward and backward to the max- 

 illary, in which it is continued to beneath the orbit. The malar 

 bone, 26, is long and deep, especially below the orbit, of which it 

 forms the lower half; and where it bends outward to expand that 

 cavity, it unites with the lacrymal and extensively with the max- 

 illary anteriorly, and bifurcates behind, — the narrower branch 

 mounting to the postorbital, the broader one continuing back- 

 ward to the squamosal, 27. This essentially facial or maxillary 

 element is anchylosed not only with the mastoid and petrosal, but 

 also with the tympanic ; its cranial plate terminates by a convex 

 border overlapping the contiguous borders of the alisphenoid and 

 parietal. The articular surface for the mandible is broad and 

 flat, save where its inner border bends down upon the side of the 

 petro-tympanic bulla. There is no riclge behind it to prevent the 

 free movements of the mandible backward and forward, accom- 

 panying the rodent action of the great scalpriform incisors : in 

 this the Aye-aye differs from other Lemuridcc. 



The mandible, 32, is short and deep : each ramus is compressed 

 and straight ; they converge at an acute angle to a short ligament- 

 ous symphysis. The condyle is sessile, narrow, rather long, convex 

 both across and lengthwise, and the latter most so, looking back- 

 ward and upward, and })laccd on tlic level of tlie grinding-teeth. 



