PEIMATES PEOM MADAaASCAE. 93 



horizontal ridge with the flange-like lambdoidal crest. In Propithecus a line may be 

 traced running horizontally backwards above the auditory orifice to join the superior 

 occipital ridge, suggesting the former existence of a similar crest. 



In Mesopropithecus large auditory bullae exist, similar in shape and proportions 

 to those of recent Indrisinse, and there is in old skulls a fusion of the postglenoid 

 process with the bulla. 



The Basilar Begion. — The obliteration of the sutures observed in the roof of the 

 cranium is again seen in the case of the bones forming its floor. In the oldest skulls 

 hardly a trace remains of the occipito-sphenoid, sphenoid, maxillo-palatine, or maxillary 

 sutures. The external pterygoid laminse are widely everted at their posterior margins ; 

 the glenoid fossae are broad and deep, resembling those of Palaiopropithecus. The 

 postglenoid process is broad and strong, and has also a greater vertical extension than 

 in Propithecus. 



In the palatal region we again see evidence of the stouter and more robust make of 

 the fossil form as compared with all its existing relatives. The posterior margin of the 

 palatines is three or four times as thick as in Propithecus and Indris. The central 

 portion is depressed (in the direction of the vomer) and in young animals is produced 

 into a short postpalatine spine. The forward extension of the palatine is intermediate 

 in extent between the condition seen in Propithecus and Indris. The interior part of 

 the palate is much broader than in any of the recent representatives of the subfamily, 

 the distance between the internal margin of the anterior pair of premolars being in 

 excess of that between the first molars. In all recent genera the dental series converge 

 towards the anterior part of the palate ; in Mesopropithecus they are almost parallel. 



Dentition. — The dentition of Mesopropithecus so closely resembles that of Propithecus 

 and Indris that a short comparison with these modern genera will suffice (see PL XXI. ). 

 As already stated, the inner pair of incisors in Mesopropithecus, while larger than the 

 outer, were more nearly equal than in Indris. So far as it is possible to judge from 

 the size, position, and direction of the alveoli, the incisors of Mesopropithecus were 

 intermediate in function between those of Archceolemur and Propithecus. There has 

 evidently been some variability as to the position of the external pair of incisors — 

 in one case a short diastema occurring between this tooth and the canine, while in 

 another skull the alveolus is confluent with that of the canine. The same variability 

 in the position of the outer incisor is seen in Palceopropithecus. 



The canine in Mesopropithecus is a large and powerful tooth, having a horizontal 

 extension of nearly a centimetre and a breadth of 4:"5 mm. It has a large internal 

 talon overlapped by the anterior margin of the second premolar. This latter and the 

 following tooth bear a strong likeness to the corresponding teeth of Palceopropithecus, 

 though the greater prominence of the backwardly sloping central external ridge and 

 the development of the small labial cusps ally these teeth even more closely to those 

 of Propithecus. 



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