It is to be remembered that the three nuclei we have referred to, the nucleus caudatus, nucleus lenticularis, and thalamus opticus, receive fibres from and give fibres to the internal capsule. There are fibres passing upwards to the convolutions and others downwards to the lower centres.

Passing upwards, the fibres of the internal capsule are continued into the Corona radiata or centrum ovale, containing the white substance of the hemispheres, and it may be stated generally that in the corona radiata motor fibres are anterior and sensory posterior. But besides these fibres there are multitudes which form communications between one part of the convolutions and another, and altogether the connections here are very complicated.

The Cerebral convolutions and their arrangement may be studied in Ecker's work, where the descriptions are very clear.

If the lateral aspect of one of the cerebral hemispheres be examined (see Fig. 322), two great landmarks should first be made out; these are the fissure of Sylvius (S, S, S), and the fissure of Rolando (R,B). There is no difficulty with the Fissure of Sylvius of which the main or transverse arm is perfectly distinct, while its short ascending arm near the front is easy to make out. The Fissure of Rolando passes obliquely forward from above downwards through the middle of the lateral aspect of the hemisphere to the longitudinal fissure above, but not reaching the fissure of Sylvius below. This fissure can usually be recognized by the fact that it is bounded by or lies between two convolutions which extend side by side upwards and backwards from the fissure of Sylvius (A, A, A and B, B). There is frequently, however in front of it a sulcus which may be mistaken for it.

Fig. 322. - Left lateral aspect of cerebrum. Explanation in text. (Quain).

Having distinguished these two fissures the various lobes of the brain may now be determined. All in front of the fissure of Rolando, and above the fissure of Sylvius, is Frontal lobe. The Parietal lobe lies behind the fissure of Rolando, and its posterior extremity is bounded by a fissure which is best seen on the inner face of the hemisphere, the Parietooccipital fissure. This fissure, beginning about the edge of the great median fissure, passes downwards and forwards on the inner face of the hemisphere (par. occ.f., Fig. 323). Behind this is the Occipital lobe. The remaining lobe is the Temporo sphenoidal, which lies below the fissure of Sylvius and extends backwards to meet the occipital lobe, from which it is indefinitely distinguished.

Of the convolutions the easiest to determine are those bounding the fissure of Rolando, one of which belongs to the frontal and the other to the parietal lobe; these are called the Ascending frontal and Ascending parietal convolutions respectively. In front of the ascending frontal, the frontal lobe presents three layers of convolutions (a, a', and a") which lie transversely and pass by their posterior extremities into the ascending frontal. These Transverse frontal convolutions are distinguished as the first, second, third, or superior, middle, and inferior. It is not to be supposed that these are single simple convolutions, they are rather layers or strata of convolutions. The inferior (a", a") is a very important one, and it can generally be easily recognized as it curves round the short ascending branch of the fissure of Sylvius (S). After curving round this branch it becomes continuous with the lower end of the ascending frontal. At this point the two convolutions form a somewhat triangular piece, and as this lies over and partially covers the island of Reil, it is often called the Operculum (in the position of x A in Fig. 322). In addition to these we have still in the frontal lobe the Supraorbital convolutions (a*), which have no arrangement that needs to be detailed.

In the parietal lobe the Ascending parietal convolution (B, B, Fig. 322) is already known. Another easily recognized one is that which lies immediately above the fissure of Sylvius, and is called the Supramarginal convolution. The posterior portion of this convolution curves round the upper end of the fissure of Sylvius, and as it turns thus round an angle it is often called the angular gyrus (b", b'"), and is important, as Ferrier has supposed it to be the seat of visual memory. The rest of the parietal lobe is divided into an upper and a lower portion by a longitudinally placed fissure which is often not very distinct, the intra-parietal fissure, which arises close to the fissure of Sylvius behind the fissure of Rolando to which it at first lies parallel, and then passes backwards. The lobe is thus divided into the Superior and Inferior parietal lobules, the former being continuous in front with the ascending parietal convolution.

In" the Occipital lobe, looking at the lateral aspect, three transverse layers of convolutions can be distinguished. These are named as in the frontal lobe, first, second, and third, or superior, middle, and inferior (d, d', d", Fig. 322). On the under or basal surface there are two further layers which are continuous in front with those of the temporo-sphenoidal lobe and are named in common with them inferior occipito-temporal convolutions.