60 THE CEREBRUM. 



with the supero-medial border of the hemisphere. They separate 

 from each other three gyri of nearly equal width, viz., the superior, 

 middle and inferior frontal gyri (Fig. 24). 



The superior frontal gyrus is incompletely divided in the 

 human brain by an interrupted sulcus, called the sulcus para- 

 medialis (Fig. 23) which is located near the supero-medial border 

 of the hemisphere and is said by Cunningham to be better developed 

 in the higher types of the human race and to be rare in the higher 

 apes. 



A series of shallow furrows, described by Eberstaller as the 

 middle frontal sulcus (s. frontalis medius, Fig. 23) partially sub- 

 divides the middle frontal gyrus into an upper and a lower part. 

 The middle frontal sulcus, not found below the anthropoid apes 

 (Cunningham), is best marked anteriorly and, at the superciliary 

 border of the hemisphere, bifurcates and forms a horizontal 

 furrow, the fronto-marginal sulcus. The posterior end, the 

 foot, of the middle frontal gyrus, like that of the superior and 

 inferior frontal, lies in the psychic-motor zone of the brain. It 

 contains the writing center (Gordinier) in the left hemisphere 

 of right-handed people. 



The inferior frontal gyrus is highly developed in the human 

 brain, especially in the left hemisphere of right-handed people. 

 It is deeply cleft along its lower border by the anterior ascending 

 and anterior horizontal rami of the lateral fissure of the cerebrum 

 and is thus divided into a pars orbitalis, situated below the anterior 

 horizontal ramus, a pars triangularis, inclosed between the ante- 

 rior horizontal and ascending rami, and a pars basilaris, located 

 between the anterior ascending ramus of the lateral fissure and 

 the inferior precentral sulcus. The pars basilaris constitutes the 

 foot of the inferior frontal gyrus and is continuous with the gyrus 

 centralis anterior; on the left side it contains the speech center. 

 The anterior portions of the superior middle and inferior frontal 

 gyri comprise a psychic center, center of attention, volition, in- 

 hibition, etc., "of abstract concept" (Mills). 



The anterior central gyrus (g. centralis anterior} lies between 

 the precentral sulci and the central sulcus. It is joined to the 

 posterior central gyrus by the paracentral lobule, above the 



