440 ^\■. K. GREGORY NOTHARCTUS AND LEMUROIDEA 



with a ivliiii\c mliR-tioii ill size of the orbits and of the volume of the 

 lu-aiii: 111 MIrrarcbn.s, on the contrary, there may have been a dwarfing 

 ,,r li(.(l\ size, a -ivat widening of the brain, a reduction of tlie face, and 

 ill! ,.|ihii-viiiciit (.r the orbits. In many lines the lower jaw orcw lon^- 

 and weak, tiic alible slender: the lower incisors and canines became small, 

 l.rociimlM'iit ami compressed: the muzzle was often widened: the upper 

 incisors weiv rechiced; the opposite tootJi rows straightened. The molars 

 were tlivci-sely modified, some becoming blunt-cusped with low, round 

 cingulmii. others becoming sharp-cusped with cuspidate cingulum. The 

 limbs and extremities, which were primitively short, as in Lepilemur, 

 either grew long and slender, as in Microcehus, which has the tarsus 

 variously elongate, or stout and relatively short, as in the hind limb of 

 Megaladapis. Tlie writer is convinced that changes in the direction of 

 evolution involving reversal of proportions, such as large orbits changing 

 into small orbits, expanded bullae becoming deflated, and the like, have 

 been frequent in the history of the Lemuroidea. 



The Indrisine lemurs, or Indrisidse, constitute a very well marked 

 Malagasy group which may have been derived from a form like Proni/rii- 

 rehm of the Adapina3 by the expansion of the orbits and brain-case, very 

 marked shortening of the face, great deepening of the lower jaw and its 

 angle, and crowding out of two premolars above and below on each side, 

 namely, pmV, pm" and pm^, pnig ; at the same time the upper molars 

 became elongate anteroposteriorly ami the cingulum grew u]) into a large 

 hypocone in adaptation to leaf- and fruit-eating habits. The basicranium, 

 including the bullfe and the course of the internal carotid artery, were 

 fundamentally similar to those of the Ada})id[e and Lemuridge, and the 

 same is true of the backbone, limbs, placentation, and brain. This primi- 

 tively central and relatively high type is most nearly realized in the 

 existing genus Avahis, which has, however, further expanded the brain 

 and orbits. A retrogressive series leading in a general way througli 

 Mesopropithecus and Indris ends in the highly aberrant and misnamed 

 PalcepropitJiecus — a gross and swinelike animal, with a thick muzzle, 

 small eyes, deflated bullfe, and a low brain-case. Al)oiit i\\Q only feature 

 ill whicli Palceprqpithecus is not degraded is the extreme depth of its 

 lower jaw, in which it surpasses all the otker Indrisinse. 



Tn the opposite direction a progressive series, in which only the ter- 

 minal memljers are known, has led from tlie primitive Indrisine to the 

 apelike NesopUlmcns (Archceolemur) and the still more advanced Uadro- 

 pWiecus. These forms, by reason of their large brain-case, forwardly 

 directed orbits, and macaque-like molar teeth, have given rise to the 

 preposterous liypothesis that they indicate a special affinity between the 



