THE BRAIN. 185 



ponding portion of the opposite lobe by the falx cerebri, 

 and is marked off from the rest of the internal surface by 

 the callosomarginal fissure. 



The frontal lobe presents three well-marked tertiary 

 fissures : the superior and inferior or first and second 

 frontal sulci which run anteroposteriorly, and the pre- 

 central, which is at right angles to the above, and irregu- 

 larly parallel to the fissure of Rolando. The last fissure 

 is usually interrupted in its course, and the anteroposterior 

 sulci may terminate in it ; the superior usually does. 



These sulci divide the frontal lobe into four convolu- 

 tions : The ascending* frontal, which lies parallel with and 

 in front of the fissure of Rolando, and is limited in front 

 by the precentral fissure. The superior frontal convolu- 

 tion, which becomes continuous on the inner surface with the 

 marginal convolution, on the inferior surface with the inter- 

 nal convolution, and behind with the ascending frontal convo- 

 lution. The middle frontal convolution, between the 

 superior and inferior frontal sulci, is extended around to the 

 inferior surface of the frontal lobe, and backward to the pre- 

 central -sulcus, by which it is separated from the ascending 

 frontal convolution. On the under surface of the lobe this 

 convolution merges into the middle or the anterior convolu- 

 tion. The inferior frontal or Broca's convolution is 

 below the inferior sulcus, arches over the vertical limb of 

 the Sylvian fissure, and becomes continuous behind with 

 the ascending frontal, and on the under surface of the frontal 

 lobe with the posterior orbital convolutions. This convolu- 

 tion is deeply indented on its under surface by the vertical 

 limb of the fissure of Sylvius, and above by the precentral 

 sulcus. 



The internal and inferior surfaces will be described on 

 pages 1 88 and 192. 



