104 EINAR LONNBERG, MAMMALS COLLECTED BY THE SWEDISH ZOOLOGICAL EXPEDITION ETC. 
In the smaller and younger specimen the ascending processes of the premaxil- 
laries extend further backward beyond the end of the nasals, but in the largest 
(=oldest) specimen the nasals reach about as far back as the premaxillaries. The 
former condition prevails in Fornarina which thus in this respect represents a more 
juvenile stage than Heterocephalus. 
If Ripreny’s figure of the skull of H. glaber is correct my specimens differ 
widely from that species with regard to the situation of the palatine foramina which 
in the former are situated chiefly in front of a line drawn across the palate as a 
continuation of the pheripheric contour of the zygomatic arches. In my specimens 
these foramina are situated behind such a line in the same way as in Fornarina 
according to Tuomas’ figure’ of the latter. But, although the situation of these 
foramina thus far is alike in my specimens and in Fornarina, there is another quite 
important difference between them. In the latter, according to THomas’ figure, the 
suture between the premaxiliary and the maxillary extends across the palate at the 
anterior end of the palatine foramina, but in my specimens the corresponding suture 
is seen at the posterior end of the foramina in question. These foramina are also 
very small in my specimens their length being about 1,5 mm. 
Concerning H. dunni Tuomas writes as follows: »Incisors enormously thick and 
large, far heavier than in any other member of the group.» — — — »combined 
breadth of upper incisors 3,0>.— — — In my largest specimen the incisors are still 
larger and heavier measuring as much as 3,3 mm. As the type of H. dunni is said 
to be old and the length of its head and body is about 10 mm. more than that of 
my biggest specimen this difference in the combined breadth of the upper incisors 
appears to be of importance. The size of the incisors in H. glaber appears to be 
rather constant and not increase much with age, because Tuomas says that the 
study of immature and old specimens of that species has shown to him »that no such 
development of the incisors occurs in old age in that animal». That is, the incisors 
do not increase in size with age so that they become so big as those of H. dunni. 
In the present specimens on the other hand, a very striking increase in size of these 
teeth takes place. In the smallest and youngest of my specimens the combined 
breadth of both incisors is only 2,1 mm., in the next 2,4 mm., in the third 2,8 mm., 
and in the biggest 3,3 mm. If only one of these younger and smaller specimens, and 
the biggest had been collected, it would have appeared rather probable that these 
specimens represented two different races, a small and a large, because the dissimil- 
arity is so very obvious and even the smaller looks rather adult thanks to its lamb- 
doid crest. With the intergradation exhibited by all four specimens it is impossible 
to believe in such a theory, and the gradual development of the incisors is quite 
clear. But then, when nothing of that kind of development is to be seen in H. glaber 
as quoted above, these specimens cannot be referred to that species. Other differences 
from the same, in addition to different shape of the zygomata and the situation and 
size of the palatine foramina, are the greater length of the nasals, the longer diastema 
and the greater occipitonasal length of the skull. 
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