1936] Hatt, Hyraxes Collected by American Museum Congo Expedition 121 



Fontanel and Wormian Bones 



Fontanel and wormian bones occur with relative frequency in the 

 Congo Expedition series of Procavia j. lopesi. None were found in the 

 skulls of Dendrohyrax d. emini, the early closure of the cranial sutures 

 being unfavorable to their recognition, even should they be present in 

 early life. In this respect these two species are representative of their 

 generic groups, for fontanel and wormian bones are about four times as 

 frequent in occurrence in Procavia as in Dendrohyrax. 



The hypothesis advanced by Schultz (1923, Journal of Mammalogy, 

 IV, p. 65) that these bones are neomorphs in the mammalia that appear 

 at places in which the normal roofing-over process is inadequate to meet 

 demands of protection, receives some slight support from these findings, 

 for in the hyraxes these accessory ossicles occur with greatest frequency 

 in the group with the most retarded solidification of the skull roof, and 

 most rarely, if one may judge from examination of a series that contained 

 few skulls with open parietal sutures, in the group in which early 

 closure is the rule. 



The incidence of occurrence in the three genera, as determined from a 

 survey of all skulls of hyraxes in the American Museum, is as follows : 



Number of 









Skulls with 











Wormian or 







Total Number 



Fontanel 





Genus 



of 



Skulls 



Bones 



Incidence 



Procavia 





53 



8 



15.1% 



Heterohyrax 





34 



3 



8.8% 



Dendrohydrax 





78 



3 



3.7% 



All forms 





165 



14 



7.8% 



The two species of Congo hyraxes represented by series show slightly 

 different percentages than do the larger groups considered. Thus Pro- 

 cavia j. lopesi has five cases of accessory roofing bones in 22 skulls, 

 an incidence of 30 per cent, whereas no case (unless a single Stage I skull 

 in which the interparietal bears a median suture should be considered an 

 exception) occurs in 37 skulls of Dendrohyrax d. emini. 



The sexual distribution of extra bones in the mid-line was approxi- 

 mately equal, there being 6 males and 7 females showing the variant. 



Asymmetry 



Asymmetry is not a character of the Hyracoidea and no case of well- 

 marked asymmetry in the skulls of Congo hyraxes has been encountered 



