xii JouRNAL OF CoMPARATIVE NEUROLOGY. 
most generalised mammals, Erinaceus and FPerameles. It is a very 
constant and precocious sulcus in all the Carnivora, Ungulata, Eden- 
tata, Cetacea, and many Rodents and Galeopithecus. Most writers call 
it ‘‘presylvian” in all these non-Primate orders, but there can be little 
doubt as to its homology with the orbital sulcus, although, so far as I am 
aware, such an interpretation has never hitherto been suggested. But 
it would be strange if this (the most widespread and constant) suleus of 
the neopallium should not be represented in the Primates, and there is 
no other furrow of sufficient constancy in the pararhinal region to 
represent the presylvian sulcus of other mammals. If moreover we 
compare such brains as those of Dolichotis (Rodent), Galeopithecus (In- 
sectivore), Bradypus (Edentate), and Phascolomys (Marsuipial) with the 
Lemur’s, it is clear that the ‘‘presylvian” sulcus of the former can be 
represented in the Prosimiz only by the orbital or the fronto-orbital 
sulcus. Of these the former is not only by far the more constant of 
the two sulci, but it is also that which occupies the same position and 
relationship to the rhinal fissure as the ‘‘presylvian.’’ A comparison 
of Galago and Dolithotis shows this. 
If again we compare the behavior of the orbital sulcus in the larger 
Ungulates (e. g., the camel, horse, and ox) and Carnivores (e. g., the 
Seals), we shall find that as the hemisphere increases in magnitude (and 
more especially if at the same time it becomes more microsmatic) the 
‘‘presylvian” sulcus becomes relegated to a position alongside the anterior 
rhinal fissure exactly analogous to that occupied by the orbital sulcus 
in the Gorilla’s brain. In man the simple linear orbital sulcus becomes 
complicated by numerous side branches so as to form triradiate, 
H-shaped or other patterns; but if a large number of human brains be 
examined, the orbital sulcus will be found to consist in a very consider- 
able proportion of these cases of a single deep linear sulcus, the 
apparent branches of which are mere shallow furrows of little importance. 
Not unfrequently this sulcus joins a small anterior rhinal fissure—thus 
completing the resemblance to the junction of the ‘‘presylvian” sulcus 
with the rhinal in the Carnivora and others. 
The coronal sulcus of the non-Primate mammals may be repre- 
sented in the inferior frontal and the inferior precentral sulci of Man. 
One of the earliest sulci to make its appearance in the developing Car- 
nivore and Ungulate brain is the coronal. In the Carnivores it often 
joins the lateral sulcus, in many Ungulates it is linked to the suprasyl- 
vian, in the Pig-family it is united with the intercalary sulcus. In the 
Primates the so-called sulcus rectus exhibits a similar precocity, and 
occupies a position not unlike that of the coronal in the Ungulates and 
the primitive Viverrine Carnivores. It becomes split up in the Cebide 
and Cercopithecide into two parts, the sulcus rectus (sensu stricto) and 
the sulcus arcuatus. ‘The former develops into the inferior frontal and 
the latter into the inferior precentral sulcus. 
The problem of the exact interpretation of the central (Rolando’s) 
sulcus presents many difficulties. ‘There can be no doubt whatever as 
to the homology of the mammalian lateral with the intraparietal sulcus 
of the Primates, and the interpretation of the ansate as the 
