652 THE NERVOUS SYSTEM. 



4. The temporal lobe, sometimes called the temporo-sphenoidal lobe, presents 

 an outer and an inferior surface. The outer surface is subdivided by two fissures, 

 named respectively the first and second temporal sulci. The first temporal sulcus 

 is well marked, and runs from before backward through the temporal lobe 

 parallel with, but some little distance below, the horizontal limb of the fissure of 

 Sylvius, and hence is often termed the parallel sulcus. The second temporal sulcus 

 takes the same direction as the first, but is situated at a lower level, and is often 

 interrupted by one or more bridging convolutions. These two sulci subdivide this 

 surface of the temporal lobe into three convolutions. The Jirst or superior tem- 

 poral convolution is situated between the horizontal limb of the fissure of Sylvius 

 and the first temporal sulcus, and is continuous behind with the supra-marginal 

 convolution. The second or middle temporal convolution lies between the first 

 and second temporal sulci, and is continued behind into the angular and middle 

 occipital convolutions. The third or inferior temporal convolution is placed below 

 the second temporal sulcus : it is connected posteriorly with the inferior occipital 

 convolution, and is also prolonged on to the under or tentorial surface of the 

 temporal lobe, where it is limited internally by the third temporal sulcus, about 

 to be described. 



The inferior or tentorial surface presents two fissures, viz. : the third temporal 

 sulcus and the collateral fissure the latter of which has already been described 

 (page 647). The third temporal sulcus extends from near the occipital pole 

 behind, to near the anterior extremity of the temporal lobe in front, but is, how- 

 ever, frequently subdivided by bridging gyri. The convolutions on the inferior 

 surface are (1) the fourth temporal or subcollateral convolution (sometimes called 

 the external occipito-temporat), situated between the third temporal sulcus and the 

 collateral fissure ; and (2) the subcalcarine convolution or lingual lobule, lying 

 between the calcarine fissure above and the posterior part of the collateral fissure 

 below and continuous in front with the hippocampal convolution, the latter forming 

 part of the lirnbie lobe. 1 



The central lobe or island of Reil (Fig. 349) lies deeply in the Sylvian fissure, 

 and can only be seen when the lips of that fissure are widely separated, since it is 

 overlapped and hidden by the convolutions which bound the fissure. These 

 convolutions are termed the opercula of the insula ; they are separated from each 

 other by the three limbs of the Sylvian fissure, and named the orbital, frontal, 

 fronto-parietal, and temporal opercula. It is almost surrounded by a deep 

 limiting sulcus, which separates it from the frontal, parietal, and temporal lobes. 

 When the opercula have been removed, the insula presents the form of a triangular 

 eminence; its apex is directed downward and inward toward the anterior 

 perforated space, and is continuous in front with the posterior orbital convolution 

 and behind with the hippocampal convolution. It is divided into a pre-central 

 and a post-central lobe by the sulcus centralis, which runs backward and upward 

 from the apex of the insula. The pre-central lobe is further subdivided by 

 shallow sulci into three or four short convolutions, the gyri breves, while the 

 post-central lobe is named the c/yrus longus and is often bifurcated at its upper 

 extremity. The gray matter of the insula is continuous with that of the different 

 opercula, while its mesial surface corresponds with the lenticular nucleus of the 

 corpus striatum. 



Limbic Lobe. The term limbic lobe (grande lobe limbique) was introduced 

 by Broca in 1878, and under it he included two convolutions, viz., the callosal 

 and hippocampal, which together arch round the corpus callosum and the 

 hippocampal fissure. These he separated on the morphological ground that 

 they are well developed in animals possessing a keen sense of smell (osmatic 



1 It will be seen from this description that the tentorial surface of the occipital lobe is regarded 

 as forming part of the same surface as the temporal lobe. Tbe boundary between the 

 occipital and temporal lobes on the tentorial surface is purely artificial, and if represented by a 

 line drawn upward and inward from the pre-occipital notch, would cut both the subcollateral and 

 subcalcarine gyri. 



