42 EINAR LÖNNBERG, MAMMALS COLLECTED IN CENTRAL AFR1CA. 



nasals form a median rounded ridge, on either side bordered by a broad shallow groove, 



011 tlie outside of which the now compact lateral ridges rise as a crowning of the vertical 

 side walls of the maxillary. The whole upper surface of the snout ridges has gotten an 

 uneven and rugged appearance, and the compactness of the bones indicates their value 

 as protective armature. 



The nasals are very different in shape at different ages. In the young animal with 

 only milk-dentition the anterior portion of the nasals, which already are f ully anchylosed 

 without any visible mesial suture, is broadly triangulär measuring 11 mm. in breadth 

 at the nasal opening, or not much less than in the old male. This triangulär portion has 

 about the same length as breadth, but the nasals are then produced backwards as very 

 narrow linear strips of bone, only measuring about 2 mm. together in the interorbital 

 region. These posterior narrow parts of the nasals are not yet coossified but show an 

 open mesial suture. This suture has alredy disappeared in the next stage with the first 

 molar developed. At the same time the shape has altered so that the nasals do not any 

 longer form a broad anterior triangle with a narrow posterior shaft, but they taper 

 more gradually backwards, because the middle and posterior portions have grown some- 

 what in breadth. The development of these bones has continued in the same direction 

 in the next stage with the second molar developed. In the fully adult male the greatest 

 anterior breadth of the nasals is 13,8 mm. and 28 mm. from the anterior end it is still 



12 mm. On a level with the centre of the orbit it is 6,4 mm. These measurements com- 

 pared with those indicating the length of these bones, and which are recorded in the table 

 above, show the gradual transformation of the nasals. With the increasing breadth of 

 the posterior parts of the nasals they are also thickened, and at the same time rising 

 above the surroundning bones. It has already been stated that the nasals of the female are 

 flat. In their general outline they resemble those of the semiadult male with the second 

 molar developed. 



With regard to the development of the skull at the different ages represented it 

 can be concluded from several of the series of measurements in the table that it is chiefly 

 the facial portion which grows, while the brain-case increases less in size (ef. Pl. VII). 

 The breadth of the brain-case of the young male with milk-dentition is already fully 88 % 

 of that of the adult male. In a similar way there is only a difference of about 4 mm. 

 between the least postorbital width of the young with milk-dentition and that of the adult 

 male. The length of the brain-case is not so easy to measure exactly, but if this is attempt- 

 ed by taking the distance from the mesial point of the superciliary ridge to the occiput 

 (not counting the occipital crest of the adult) we find that this dimension of the young 

 with milk-dentition represents nearly 77 % of the whole length of the skull, and it is 85,7 % 

 of the length of the brain-case of the adult male, which in the same measures less than 

 half the total length of the skull. If the skull with the first molar developed is compared in 

 this respect with the adult, we find that the corresponding percentage is not less than 92,3 % 

 To fully estimate this it must be remembered that the total length of the skull of the 

 young animal with milk-dentition is only 56,9 % of that of the adult, and the total length 

 of the skull with the first molar developed is 66,4 % of the adult. 



Quite opposite relative conditions are found if such measurements as express the 



