282 " PRACTICAL ANATOMY. 



second, and third ; three orbital, first, internal; second, 

 external ; third, posterior ; six convolutions in the island 

 of Reil, and five on the inner surface of the cerebrum, 

 the marginal, quadrate, cuneate, fornicate, and uncinate. 

 There are three primary fissures on the outer surface of 

 the cerebrum, namely, the fissure of Sylvius, fissure of 

 Rolando, and parieto-occipital. The fissure of Sylvius 

 is first formed. It is found well developed in the entire 

 range of vertebrate brains. In man it passes upward from 

 the base of the anterior third of the brain, runs upward 

 and backward for three-fourths of an inch, and divides 

 into an ascending and a horizontal limb. The stem of 

 the fissure of Sylvius separates the frontal from the 

 temporo-sphenoidal lobe. The fissure of Rolando passes 

 downward and forward from the upper part of the great 

 longitudinal fissure, and terminates just above the angle 

 of division of the fissure of Sylvius. It separates the 

 frontal lobe from the parietal. The parieto-occipital 

 fissure separates the parietal from the occipital lobe. 

 It is placed at the posterior third of the longitudinal 

 fissure, and passes downward between the superior 

 parietal and the first occipital convolution. On the 

 inner surface of the hemispheres it is better developed, 

 and extends downward between the quadrate and 

 cuneate convolutions and terminates in the calcarine 

 fissure. 



THE CONVOLUTIONS OF THE FRONTAL LOBE. 



The superior, middle, and inferior are short, hori- 

 zontally-placed gyri, connected by short annectant or 

 secondary convolutions, and separated by the superior and 

 inferior frontal fissures. The ascending frontal is a long, 

 obliquely-placed convolution, which lies between tlje 

 vertical limb of the fissure of Sylvius in front and the 

 fissure of Rolando behind. 



