TEMPORAL LOBE. 525 
the cerebral fissure. It is apparently the only part which is developed in the ape, and often also 
it is the only part which is present in the brain of the microcephalic idiot. It is not uncommon, 
in the normal cerebrum, to find that it presents an ape-like form and is completely cut off from 
the posterior part of the fissure. The posterior calcarine fissure is a secondary formation. It 
appears much later, and usually in two pieces, which run together and then join the anterior 
ealearine fissure. The points of union are indicated in the adult by the two cuneo-lingual deep 
gyri. The posterior calcarine fissure is a purely human characteristic; it is not found in any 
ape, and is usually absent also in the more intense forms of microcephalic idiocy. 
The cuneus is the wedge-shaped or triangular district, on the mesial aspect of 
the occipital lobe, which lies between the internal parieto-occipital and calcarine 
fissures. 
The gyrus lingualis is a well-marked convolution between the calearine fissure 
above and the posterior part of the collateral fissure below, which stretches 
forwards from the occipital pole. Anteriorly, it becomes very narrow and joins the 
hippocampal part of the limbic lobe. It hes partly on the mesial surface and 
partly on the tentorial surface of the occipital lobe. 
On the tentorial surface of the occipital lobe there is only one convolution, 
viz. the posterior part of the occipito-temporal gyrus. It proceeds continuously 
forwards into the temporal lobe on the outer side of the collateral fissure, and is 
bounded externally by the occipito-temporal sulcus, a furrow which is rarely con- 
tinuous, but is usually represented by a series of detached pieces. 
There are two well-marked sulci on the external surface of the occipital lobe, 
viz. the sulcus occipitalis transversus and the sulcus occipitalis lateralis. The sulcus 
occipitalis transversus extends transversely across the upper part of the lobe, behind 
the arcus parieto-occipitalis. As already explained, it is the terminal bifurcation of 
the ramus occipitalis of the intraparietal sulcus. The sulcus occipitalis lateralis is a 
short horizontal furrow, which divides the outer surface of the lobe into an upper 
and a lower area of very nearly equal extent. These areas are connected by super- 
ficial annectant gyri with the parietal and temporal lobes. 
TEMPORAL Lospe.—The temporal lobe lies behind the stem and below the 
posterior horizontal limb of the Sylvian fissure. It is somewhat pyramidal in form, 
and presents an upper, an outer, and a tentorial surface, with a free projecting apex 
or pole. Above, it is bounded by the posterior horizontal limb of the fissure of 
Sylvius, together with the artificial line which is drawn backwards from this. On 
the tentorial face it is separated from the hippocampal part of the limbic lobe by 
the collateral fissure, whilst behind it is marked off from the occipital lobe by the 
artificial lines already described. The temporal pole projects forwards on the under 
surface of the brain beyond the stem of the Sylvian fissure. It should be noticed 
that the recurved end of the hippocampal part of the limbic lobe (uncus), which lies 
to the inner side of the temporal pole, does not extend so far forwards as the latter, 
and is separated from the pole by the incisura temporalis. This sulcus may be 
regarded as the connecting link between the anterior end of the collateral fissure 
and the inferior limiting sulcus of Reil. The importance of this connexion is 
evident when we recollect that, strictly speaking, the inferior limiting sulcus of 
Reil is the true upper limit of the temporal lobe. 
The upper or opercular surface of the temporal lobe is turned towards the 
island of Reil and the fronto-parietal operculum. ‘The fissure of Sylvius must, 
therefore, be widely opened up to expose it. For the most part the surface is 
smooth, but towards the back part there are a few transverse furrows, which 
separate two or three weakly-expressed gyri. 
The anterior transverse gyrus is much more strongly expressed in the foetal than in the adult 
brain. It appears in the early part of the seventh month, and is only subsequently completely 
hidden within the Sylvian fissure. The fact of the auditory centre being localised in this region 
of the temporal lobe makes this fact of interest. 
On the deep surface of the temporal pole there are also a few feeble furrows. 
On the outer surface of the temporal lobe there are two horizontal sulci, 
called respectively the first temporal or parallel and the second temporal sulcus. 
The parallel sulcus is a long, continuous, and deep fissure, which begins near the 
temporal pole and proceeds backwards below the posterior limb of the Sylvian 
