The precentral and postcentral sulci are about 15 mm. (3/5 in.) anterior and posterior to the fissure of Rolando.

The inferior frontal convolution lies between the line of the fissure of Sylvius below and a line just below the temporal ridge above.

The middle frontal convolution lies under the frontal eminence, and occupies about the lower two-thirds of the distance between the temporal ridge below and the midline above.

Fig. 50.   Semidiagrammatic view of head, showing relation of Rolandic and Sylvian fissures and lines.

Fig. 50. - Semidiagrammatic view of head, showing relation of Rolandic and Sylvian fissures and lines.

The superior frontal convolution covers about the upper one-third of the distance from the median line above to the temporal ridge below.

The superior frontal sulcus passes upward from the supra-orbital notch.

The inferior frontal sulcus runs just below the temporal ridge.

The first or superior temporal convolution runs along the lower side of the fissure of Sylvius. It is about 15 mm. (3/5 in.) wide.

The first or superior temporal sulcus or parallel fissure runs parallel to the Sylvian fissure and 15 mm. below.

The second or middle temporal convolution is wider than the first and lies a short distance above the level of the base of the skull.

The middle temporal sulcus runs close above the zygoma.

The third or inferior and the fourth temporal convolutions lie on the base of the brain, separated by the inferior temporal sulcus. The fourth temporal convolution has on its inner side the collateral fissure (see Fig. 42).

The interparietal sulcus (pars horizontalis) leaves the postcentral sulcus near its middle and passes upward and backward to a point opposite the lambda.

The supramarginal convolution surrounds the termination of the fissure of Sylvius and is, therefore, under the parietal eminence.

The angular gyrus surrounds the posterior end of the first temporal sulcus (parallel fissure) and is, therefore, 3 or 4 cm. (1 1/4 to 1 1/2 in.) posterior to the parietal eminence.

The transverse occipital sulcus is a continuation of the interparietal sulcus to just beyond the parieto-occipital fissure.

The lateral occipital sulcus lies close to the tentorium; it divides the occipital lobe into superior and inferior convolutions. (Sometimes these two sulci divide the lobe into three convolutions, superior, middle, and inferior).

The Fissures In Children

In childhood the fissure of Rolando is somewhat more vertical than in adults; the fissure of Sylvius has its point of division a little higher and runs up to and usually above and in front of the parietal eminence (Dana, Med. Record, Jan. 1889, p. 29). After the age of three years, the relative position of the fissure to the parietal eminence begins to approach that of the adult. (For variations due to age see Cunningham: " Contributions to the Surface Anatomy of the Cerebral Hemispheres," 1892).

The objects of cerebral topography are mainly to ascertain in case of injury or disease of the superficial structures what parts of the brain beneath are liable to be involved, and for operative procedures, in order to expose the affected areas. The convolutions and sulci are so variable that all guides are only approximate. In order to overcome this defect and provide for unusual conditions, the openings in the skull are usually made quite large. The flaps of scalp and bone may even embrace the entire parietal bone or a quarter of one hemisphere. As regards the various points - the upper Rolandic point is generally conceded to be 15 mm. (1/2 to 5/8 in.) posterior to the midpoint between the glabella and inion. The angle which the fissure forms With the median line varies from 64° to 750. Cunningham gives it as 700 and Arthur W. Hare as 670. Chiene's method of finding the desired angle is usually accepted as reliable. He takes a square piece of paper and folds it obliquely from corner to corner making 450, and then folds it a second time making 22 1/2°. The two being added together give 67 1/2° as the angle made by the fissure of Rolando with the anterior portion of the longitudinal fissure.

The pterion was placed by Broca at the coronal suture. This is 15 mm. (3/5 in.) in front of the Sylvian point. In several formalin hardened brains, we found this latter to be at the posterior angle of the pterygoid wing, and in twenty measured skulls the Sylvian point averaged 42 mm. (1 5/8 in.) behind the angular process. Reid placed it at 50 mm. (2 in.), which we think too much. Anderson and Makin placed it at 1 1/2 to 2 in. Thane and Godlee placed it 35 mm. back and 12 mm. up, which is just a trifle farther forward than we have located it. Landzert and Heffler gave it as at the summit of union of the great wing of the sphenoid with the temporoparietal suture, as we have given it. When prolonged, the Sylvian fissure sometimes crosses the median line 1.5cm. (5/8 in.) above the parieto-occipital fissure, but more usually we have found it to be close to the fissure, which agrees with Reid. The parietooccipital fissure has been located by some authors near the lambda, but we would place it 1.5 cm. (5/8 in.) above. We believe the parietal eminence to be a fairly reliable guide to the posterior extremity of the fissure of Sylvius. Method of Anderson and Makin for Locating the Fissures of the Brain. - For the sake of comparison the following method of Wm. Anderson and George Henry Makin (four. Anat. and Phys., vol. xxiii, 1888-89, p. 455) is given. Draw a mid- or sagittal line from opposite the highest point of the supra-orbital arches to the external occipital protuberance. From the midpoint on this line draw another to the pre-auricular point at the level of the upper border of the meatus. This is the frontal line. From the most prominent point of the external angular process draw a line to the junction of the middle and lower thirds of the frontal line and prolong it 1 1/2 in. beyond.

Fig. 51.   Chiene's method of folding a square piece of paper in order to obtain an angle of 67 1/2 degrees.

Fig. 51. - Chiene's method of folding a square piece of paper in order to obtain an angle of 67 1/2 degrees.

Fig. 52.   Method of Anderson and Makin for locating the fissures of the brain.

Fig. 52. - Method of Anderson and Makin for locating the fissures of the brain.

The Sylvian fissure begins between 1 1/8 and 1 1/2 in. behind the angular process or 5/12 of the distance between that point and the frontal line. The bifurcation is 1 1/2 to 2 in. behind the angular process or 7/12 of the distance between it and the frontal line, the fissure then runs to an equal distance behind the frontal line, and up for 1/2 in. parallel to the frontal line. The fissure of Rolando runs from a point 3/8 in. behind the midsagittal point to one 3/8 of an inch in front of the intersection of the frontal line and line of the Sylvian fissure. The parieto-occipital fissure is 7/12 of the distance from the midsagittal point to the inion. It lies near the apex of the lamb-doid suture.