aoe DAVIDSON BLACK 
horse this constellation is so constant and well marked that it 
has frequently been wrongly described as the ectosylvian sulcus. 
The suprasylvian, coronal and presylvian sulci in the horse 
are usually in continuity as in this specimen, a condition which 
begins early in foetal life (5). The presylvian area in the horse 
is marked by an irregular sulcus, which is quite constantly 
present and has been termed the intraorbital sulcus (5) and 
Qi p.293): 
Reference to figure 16 renders further description of the speci- 
men unnecessary in the present connection. 
DISCUSSION 
Arcuate constellation 
The first point which requires consideration is the relation of 
the furrow which has been described in the foregoing account 
as the ‘arcuate constellation,’ to the ectosylvian are. 
Several authors, among whom may be mentioned Flatau and 
Jacobson (12), Sisson (27) and Bradley (5), have noted this 
sulcus in such forms as it occurs and have termed it the ectosyl- 
vian. It may be added that this sulcus is figured by Ellenberger 
and Baum (8, p. 779) and by Chauveau (6, p. 787) in the horse, 
but in neither case has it been given a name. 
The error in using the term ‘ectosylvian’ as applied to this 
‘arcuate constellation’ becomes apparent, however, when the 
following facts are considered. 
Holl (20), Elliot Smith (9, p. 309 and elsewhere) and Kap- 
pers (l.c., supra), have already demonstrated that the pseudosyl- 
vian sulcus in ungulates is not at all homologous to the sulcus 
bearing the same name in carnivors. In the former group this 
sulcus is the result of either the partial or the complete submerg- 
ence of the first arcuate or ectosylvian gyrus. The ectosylvian 
sulei are thus incorporated in the formation of the ungulate 
pseudosylvian suleus, and depending upon the degree of oper- 
culation, are more or less hidden for a considerable part of their 
extent (figs. 10 to 13). 
Anteriorly, however, the frontal extremity of the ectosylvian 
suleus usually forms the well marked fissure termed the ramus 
