194 ANATOMY OF THE CENTRAL NERVOUS SYSTEM. 



anterior central convolution, the frontal lobe, is divided by two fissures, the 

 superior and inferior frontal sulci, into three gyri: the superior, middle, and 

 inferior frontal gyri. These convolutions are not always sharply separated 

 from one another along the entire extent of the frontal lobe, inasmuch as 

 the fissures are frequently interrupted after a short course by annectant gyri. 

 These three divisions of the frontal lobe, lying above one another, are readily 

 found on all brains. It will probably be observed also that they are con- 

 nected with the anterior central convolution by means of several annectant 

 gyri. From the central convolution, they are separated by a fissure, the 

 sulcus prcecentralis, of variable length and depth. Besides an inferior, more 

 constant, part, this sulcus has a shorter superior part, which is demonstrable 

 at times. According to the investigations of Schnopfhagen, the relation 

 here shown diagrammatically in Fig. 130 is said to be the most common one. 



On the broad middle convolution of the frontal lobe there has lately been dis- 

 tinguished a mesial, from a lateral, division. The inferior frontal convolution is in- 

 cised by the two short anterior branches of the fissure of Sylvius. They join the 

 main horizontal limb in the form of a V. This V-shaped region is the portion of 

 the gyrus designated as the pars opercularis. Considerable variations occur at this 

 point, which depend on the degree of intellectual development of the individual. 

 That portion is especially subject to variations which lies between the posterior arm 

 of the V and the anterior central gyrus: the pes of the inferior frontal convolution. 

 It is a, simple convolution, which often shows indentations, extensions, etc. On the 

 brain of Gambetta, a famous orator, it consisted of a double convolution on the left 

 side. 



The brain of the anthropoid apes is surprisingly similar, as regards convolu- 

 tions, to that of man. That whic'h especially distinguishes it from that of man, how- 

 ever, is the development of the frontal convolutions. The superior and middle gyri 

 are always very much shorter, and only rudiments of the inferior gyrus are demon- 

 strable. It is highly probable that this is the anatomical expression of inferior in- 

 telligence, particularly of the utterly undeveloped faculty of articulate speech. As 

 we probably owe the perfection of our intelligence to our faculty of speech — not as 

 individuals, but as a race — the reason for the inferior development of the entire 

 frontal lobe in apes may, perhaps, be found in the imperfect development of the 

 inferior frontal gyrus. 



The temporal lobe is traversed by several sulci, which run parallel with 

 the fissura Sylvii, and, more or less distinctly separate from one another, a 

 superior, middle, and inferior temporal gyrus. In most eases only the first 

 two of these gyri are plainly distinguishable throughout their entire extent. 



N'ow observe the region behind the central fissure and above the tem- 

 poral lobe; it is called the parietal lobe. It is divided into a superior and 

 an inferior parietal lohuh by the sulcus inter parietalis, which arches around 

 the end of the fissure of Sylvius and the first temporal sulcus. Throughout 

 most of its extent, the superior lobule is not separated from the posterior 

 central gyrus, unless, as often happens, a branch of the sulcus interparietalis 



