STUDY OF STRUCTUKE OF CENTRAL NERVOUS SYSTEM. 17 



2. The triangular area between the occipito-parietal and calearine fissures, the 

 cuneus. 



On the temporal lobe : 



Beginning above on the outer surface and counting downward there are five 

 sulci and six convolutions. The first three are called superior, middle, and 

 inferior. The inferior convolution always forms the lower edge of the temj)oral 

 lobe. 



The fourth sulcus sometimes prodiices a small elevation on the inner surface 

 of the brain, i. e., in the floor of the lateral horn, termed the collateral eminence, 

 hence the sulcus is called the collateral fissure. 



The fifth convolution is tlie hippocampus. The fifth sulcus produces the 

 hippocampus in the floor of the ventricle, hence it is called the hippocampal sulcus. 



The sixth convolution is termed the dentate fascia. 



The intimate structure of the hrain may be studied after having 

 examined its surface. By parboiling a fresh brain, the gray and the 

 white substance may be sejDarated, the gray cortex peeling off, leaving 

 the white medullary portion intact. In this way the relative thickness 

 of the cortex at any point may be determined, and the method may be 

 useful in calculating the relative amounts of gray and white substance. 



Meynert(6) says: "The structure of the cerebral cortex, like that of 

 a crystal, can be studied best from its cleavage-surface." Brains that 

 have been presented in formalin for some time are used for the purpose 

 of studying the cleavage-surface^ When siich brains are divided by a 

 sagittal cut into two hemispheres, one of the latter may be torn asunder 

 at the central sulcus of Eolando, and the break thus made passes through 

 the isthmus of the coi-pus callosum(l). 



Examination of the broken surface reveals sections of long and short fihrce 

 proprice which connect contiguous and adjacent convolutions, the decursus of tlie 

 cerebral fihers which forms the radiation of the corpus callosum and striatum, 

 and also the corona radiata and the broken ends of the arcuate fibers of the 

 cerebrum which connect the frontal lobe with other parts of the brain. However, 

 all of these structures may be seen best, by imrolling the cortex of the remaining 

 hemisphere. By rolling out the marginal convolution from above and the fornicate 

 convolution from below, the cingulum^ lies revealed and it may be traced anteriorly 

 around tlie knee of the corpus callosum into the subcallosal convolution, and 

 posteriorly around the splenium into the convolution and hook of the hippocampus, 

 connecting intermediate parts of the cortex. 



The inferior longitudinal fasciculus may be uncovered between the temporal and 

 occipital lobes. The optic radiation and the internal basal fasciculus (Burdach) 

 may be seen in the occipital lobe beneath the calearine fissure. 



Next, the convex cerebral surface is to be unfolded. 



Starting the removal of the opercula, and of the island and convolutions of 

 Reil, the lentiform nucleus is exposed with the corona radiata emanating from it. 

 The uncinate fasciculus appears and connects the frontal pole and orbital con- 

 volutions with the anterior portion of the temporal lobe. Working outward into 

 the four lobes of the brain by breaking away the cortex, the superior longitudinal 

 fasciculus is uncovered and its three terminal bundles in the frontal, occipital, 

 and temporal lobes may be seen. With special care the anterior commissure of 

 the cerebrum with its radiating connections to the cerebral lobes may be shown, 

 82307 2 



