524 DR. J. MURIE ON THE ANATOMY OF THE SEA-LION. 
parallel and equidistant from each other, being divided by single folds. Their course 
is only moderately sinuous, and throughout follows the long axis of the lobe—that is, 
have considerable upward tilt. Besides these a fourth sulcus, not ordinarily visible 
below, is met with laterally behind, or close to the occipital border. These fissures 
undoubtedly represent the three temporal ones recognized in man and the primates. 
The foremost, and possibly the one behind that, may be considered equivalent to the 
parallel or antero-temporal. The third or second and third may be regarded as mid- 
temporal; and they both merge into, and become continuous with, what I have 
described as the long limb of the Sylvian fissure. The fourth sulcus divides the post- 
temporal from the inferior occipital gyrus; it sweeps well round towards the upper 
back part of the hemisphere. As regards other occipital sulci I did not take accurate 
note. 
d. Convolutions of the outer face.-—Frontal.—Under these come those situated below, 
or the orbital series. They are simple folds lengthwise to the long axis of the brain, and 
three in number, viz. external, middle, and internal. The inferior frontal gyrus almost 
appears to be a continuation upwards of the external orbital. It chiefly forms the 
outer front lower angle of the hemisphere. and comprises a somewhat vertical and 
transverse loop-shaped fold. The midfrontal stage has similarly an upright and bent 
division. The suprafrontal tier lies alongside the margin of the hemispherical fissure, 
constituting a zigzag convolution, which appears to go back well nigh to the middle of 
the brain. Both mid- and suprafrontal gyri are in continuity; and each posteriorly 
joins the recurrent longitudinal folds of the first ascending parietal convolution. The 
short hammer-shaped crucial gyrus crops forwards on the inner anterior aspect of the 
suprafrontal convolution. 
Parietal gyri—Three in number, each possessing an ascending plication, as obvious 
a longitudinally directed one, and folds which have a lobular character terminating 
towards the posterior summit of the hemisphere. The antero-parietal begins about the 
spheno-parietal region, where no clear line of demarcation separates it from the second 
ascending plication. At the outer fronto-parietal prominence separation becomes clearer, 
the antero-parietal passing upwards behind the midfrontal, and, as above stated, becomes 
involved with the latter and the suprafrontal gyri. At the suprafrontal prominence a 
double fold wends backwards; and this, the antero-parietal convolution in proximity to 
the great marginal gyrus, continues rearwards to the internal perpendicular fissure, in 
front of which it forms a kind of lobule indented by one or two secondary short sulci. 
The postparietal convolution, as it rises from the base, is a single broad smooth fold 
which, on the side of the lobe behind the infero-frontal gyrus, has a forward knee-like 
bend. It then sweeps obliquely towards the Sylvian fissure, goes upward and parallel 
to this; and where the supramarginal gyrus turns, it again bends anteriorly. Here, 
gaining the upper surface, it wheels backwards, presenting a broad mass and subsidiary 
grooves above the supramarginal lobule; thence it continues to the occipital region, 
