412 PHYSIOLOGICAL SERIES. 



fron to-orbital sulcus between the Sylvian fissure and the 

 tri radiate orbital sulcus. When the anterior lip of this 

 sulcus becomes opercular it forms the orbital operculuni. 

 In other words, the fron to-orbital is the anterior limiting 

 sulcus of the island of Reil. 



Upon the orbital surface we always find an orbital sulcus, 

 which (as I have frequently insisted elsewhere in these 

 notes) probably represents the " presylvian " sulcus of 

 other mammals. An exceedingly variable series of com- 

 pensatory-orbital sulci develope alongside the true orbital 

 sulcus, sometimes on its mesial side, sometimes on its lateral 

 side, and often on both sides. Frequently in this way an 

 H-shaped or triradiate arrangement of sulci is formed. 

 The external compensatory-orbital sulcus often becomes 

 deep and well-defined (as in this case) to form the fronto- 

 orbital sulcus. 



The parallel sulcus extends beyond the Sylvian fissure at 

 both extremities. 



The intraparietal (lateral) sulcus arches around the apex 

 of the parallel. Its bifurcated caudal extremity the 

 transverse occipital sulcus is hidden under that peculiar 

 occipital operculum, the outgrowth of which produces 

 that great cleft known as the " Affenspalte" or " Simian 

 sulcus/' [On the left hemisphere the operculum has been 

 cut away so as to show the transverse occipital sulcus.] 



Occupying the same relation to the intraparietal sulcus 

 as the ansate does to the lateral sulcus in the Carnivora, 

 we often find in the Cercopithecidse a small ramus post- 

 centralis superior of the intraparietal sulcus. Thi> is 

 very poorly developed, especially on the right side, in this 

 specimen. 



There is a typical central sulcus. 



There is a plain sagittal sulcus rectus (the inferior frontal 

 sulcus) and a typical sulcus arcuatus (inferior precentral). 



Above the sulcus arcuatus there are two small depressions 

 representing the superior frontal sulcus. Below the central 

 sulcus there is a small plain sulcus, which EbentaUer calls 

 " inferior transverse." 



The inferior occipital sulcus is an elongated furrow the 

 upper lip of which is markedly opercular. It skirts the 



