42 Encephalic Anatomy of the Races 
of these fissures to anastomose transversely divides the corresponding 
gyres into several transverse rather than the usual longitudinal gyral 
portions. 
The subfrontal fissure is fundamentally of zygal shape, with its stem 
curving round the presylvian, and its cephalic limbs anastomosing ven- 
trad with the radiate, dorsad with a medifrontal. 
The orbito-frontal is represented by two segments; the mesial one 
anastomosing with a medifrontal. 
MerstAL SurrAcE.—The supercallosal is divided into two segments by an 
oblique isthmus. The caudal segment is confluent with the paracentral at 
considerable depth, and extends as far cephalad as the splenium. The 
cephalic segment is the larger piece, and is very much ramified. The two 
segments for a part of their course run parallel with each other, giving 
an appearance of duplication. 
The paracentral is very flexuous, 3.8 em. in length, terminating at each 
end by the usual cephalic and caudal limbs, and anastomosing caudad 
with an intraprecuneal fissure. 
The inflected fissure is deep, well-defined, and both its dorsal and mesial 
lengths are 15 mm. Its lateral end lies cephalad of the supercentral; its 
ventral end lies caudad of the cephalic paracentral limb. 
The frontomarginal is barely represented. The rostral and subrostral 
fissures are both well marked. 
ORBITAL SURFACE.—The main orbital fissure (Figure 4) is of zygal shape, 
and distinctly demarcates a post-orbital gyre, with several sagittal pre- 
orbital gyres. An independent sagittal orbital fissure lies mesad in the 
preorbital region. 
The olfactory fissure is simple, and 5 cm. in length. 
GYRES OF THE FRONTAL LOBE (LATERAL SURFACE).—The precentral gyre 
is fairly flexuous, and is quite narrow at the site of its interruption: by 
the anastomosis between the central and supercentral fissures. 
The remaining frontal gyres, especially the superfrontal and medifrontal 
are of an exceedingly complex configuration owing to the zig-zag courses 
and transverse anastomoses of the much-ramified frontal fissures. 
The subfrontal gyre in comparison with its fellow of the left side is 
small. 
MESIAL SURFACE.—The mesial surface of the superfrontal gyre is broad, 
and marked by numerous rami of the supercallosal, as well as smaller 
fissural segments. 
The paracentral gyre is about 4 cm. in length. Its dorsal border is in- 
dented by the well-marked inflected, and only slightly by the central. 
There is a vertical intraparacentral which joins the paracentral over a 
slight vadum. 
ORBITAL SURFACE.—Compared with the left half, the gyres are simpler, 
and in the preorbital region present fairly regular, sagittally directed 
gyral tiers. 
FISSURES OF THE PARIETAL AND OCCIPITAL LOBES (LATERAL SURFACE).— 
The Postcentral Fissural Complex—The confluent post- and subeentral to- 
gether measure 7 cm. in length, running parallel with the central. Sev- 
