ENDOCRANIAL CASTS OF THE GIRAFFIDAE ray Be) 
anterior ectosylvii. If, however, the frontal operculum of the 
pseudosylvian fossa be well developed, this suleus may appear 
to take its origin from the anterior rhinal fissure (compare 
fies; lOrand 13)’. 
In many cases also the posterior extremity of the ectosylvian 
sulcus appears on the surface as the ramus posterior ectosylvii. 
It is obvious therefore that this arcuate constellation present 
in certain ungulates between the processus acuminis of the 
pseudosylvian fossa and the suprasylvian sulcus, does not in 
any way represent the homologue of the similarly placed ectosyl- 
vian arch of Canidae. It is indeed peculiar to certain ungulates, 
and has no homologue among carnivors. 
It is evident that the arcuate constellation is not confined in 
its occurrence to the Giraffidae. Indeed it becomes increasingly 
manifest that the formation of this arched furrow, or series of 
furrows, is dependent upon the inter-relationship of the pseu- 
dosylvian acuminis and the suprasylvian sulcus. In the Peris- 
sodactyla, and equally in the Artiodactyla, whenever the acumi- 
nis is short and separated from the dorsally placed suprasylvian 
by a considerable interval, there appears quite constantly this 
additional arched fold, compensatory in nature, about the 
pseudosylvian region. 
In all modern Perissodactyla the processus acuminis Is usually 
separated from the suprasylvian suleus by a broad area, and in 
this group the appearance of an arcuate constellation is a constant 
phenomenon. 
In the Artiodactyla the requisite conditions for the occurrence 
of this constellation have been present among the Giraffidae 
since Miocene times. In the Camelidae on the other hand, 
these relations are of modern acquisition. 
The ancestral conditions among the Perissodactyla and in 
the Artiodactyla other than the Giraffidae and Camelidae, have 
not as yet been examined. 
Since a typical arcuate constellation has been independently 
aquired late in phylogeny among the Camelidae, it becomes 
evident that the mere presence of a well developed arcuate 
constellation in both the Fquidae and the Giraffidae is in no way 
