634 THE CEREBRUM. 



The vertical fissure of recent authors crosses the marginal convolution in the 

 posterior part of the cerebrum, extending slightly outwards upon its upper surface 

 and more deeply on its internal aspect, so as to form a separation between the 

 so-called parietal and occipital lobes. 



According to Foville the convolutions may be arranged in four principal orders, 

 founded in a great measure on their relative connections with the anterior perforated 

 space, which, in his estimation, is a part of the highest importance. 



The first order issues from the perforated space, and consists of two portions. One, 

 large and vertical, is the gyrus fornicatus, without its ascending secondary gyri ; the 

 other, short and horizontal, is the slightly elevated ridge which bounds the perforated 

 space in front and on the outer side. 



Fig. 365. RIGHT HALF OE THE BRAIN DIVIDED BY A VERTICAL ANTERO -POSTERIOR 

 SECTION (from various sources and from nature), i 



1, great superior or marginal convolution ; 2, convolution of the corpus callosum ; 3, 

 secondary convolutions running between this and the preceding ; within the numbers 

 2, 2, 2, the corpus callosum ; 4, the fifth ventricle ; 5, the third ventricle (see Fig. 377 

 for a larger view of these parts) ; 5', pituitary body; 6, immediately behind the corpora 

 quadrigemina and pineal gland; +, the fourth ventricle; 7, pons Varolii ; 8, medulla 

 oblongata ; 9, cerebellum ; the middle lobe showing the section of the arbor vitse ; I, the 

 olfactory bulb ; II, the right optic nerve ; the commissure cut through ; III, the right 

 nerve of the third pair. 



The second order, also consisting of two portions, commences from the horizontal 

 portion of the first order on the limits of the perforated space. One part corresponds 

 with the marginal convolution of the longitudinal fissure, as already described, except 

 that part of it on the orbital surface of the anterior lobe which lies to the outer side 

 of the olfactory sulcus ; the other part is the convolution of the Sylvian fissure. 



The third order consists of two sets, of which one occupies the inner surface of the 

 hemisphere, and connects the gyrus fornicatus in its whole length with the marginal 

 convolution of the longitudinal fissure ; the other set lies in the Sylvian fissure, forms 

 the island of Reil, and connects the short horizontal portion of the first order with 

 the convolution surrounding that fissure. 



The convolutions of the fourth order, the largest, deepest, and least symmetrical of 

 all, are quite detached from the perforated space, and have no relation to the first 

 order of convolutions. They connect the two convolutions of the second order 



