338 MR. W. H. FLOWER ON THE BRAIN OF MYCETES. [June 28, 
Among the Old-World Apes there is a striking general similarity 
in the character of the surface-markings of the cerebral hemisphere. 
Taking Cercopithecus as a typical form, we find Macacus, Cynoce- 
phalus, and Cercocebus agreeing with it in all essentials—a slight mo- 
dification in ascensive development in Semnopithecus and Hylobates, 
and a further complication overlying the same primitive type in T’ro- 
glodytes and Simia, leading up to the brain of Man. Among the 
New-World Apes, on the other hand, there is much greater diver- 
sity. In Cebus, but in this genus alone, there is a precise repetition 
of the Old-World type. In A¢eles a modification takes place in the 
ascending direction; but in the other forms, Pithecia, Callithria, 
Nyctipithecus, and more especially Mycetes, we have modifications 
of which there is no parallel among the Catarhine series. 
The chief peculiarities of the distribution of the sulci in the hemi- 
spheres of Mycetes are these :—1. On the outer surface: a, the ex- 
cessive prolongation of the Sylvian fissure; 0, the absence of the an- 
gular sulcus; ¢, the absence of any well-marked external perpen- 
dicular fissure. 2. On the inner face of the hemisphere: a, the 
simplicity of the calcarine fissure ; 4, the absence of any well-marked 
internal perpendicular fissure. 
In endeavouring to ascertain the zoological affinities of the genus 
Mycetes through its cerebral organization, we must first observe the 
absence of signs of serial elevation in the brain-characters (such as 
large proportionate size, and complexity of convolutions), which ought 
to be met with if the place usually assigned to it in systems, at the 
head of the Platyrhine group, be correct. Next, its great dissimi- 
larity to all, even the lowest, of the Old-World forms, and to those 
American Monkeys which in their brain-characters most closely re- 
semble the Old-World Apes. Lastly, its affinity in some of its most 
striking characters (7. e. the prolongation of the Sylvian fissure, ab- 
sence of angular and external perpendicular sulci) to some of the 
lower forms of Platyrhine Apes, as generally considered, and espe- 
cially to the genus Nyctipithecus. Whether this similarity is of 
any real zoological significance I am not prepared to say, as it must 
be taken in conjunction with numerous other structural characters. 
The general relation which is commonly supposed to obtain be- 
tween brain-structure and mental characteristics is fully borne out in 
the Howling Monkeys, all original observers of the habits of these 
animals agreeing in describing their disposition as surly and untame- 
able, and their intelligence as of a very different order from that of 
their geographical neighbours the Spider Monkeys and Cedi of 
higher cerebral organization. 
DESCRIPTION OF PLATE XXIX. 
Brain of Mycetes seniculus, natural size. 
Fig. 1. Lateral view. 
Fig. 2. Upper surface. 
Fig. 3. Under surface. 
Fig. 4. Inner face of hemisphere. 
