THE TELENCEPHALON. 



"53 



994- 



The olfactory striae, the so-called roots of the olfactory tract (Fig. 993), are 

 usually two, the mesial and the lateral, an additional intermediate root being some- 

 times represented by faint strands. The mesial stria bends sharply inward', passes 

 along the inner margin of the olfactory trigone and disappears on the mesial surface 

 of the hemisphere by joining probably partly the callosal and partly the subcallosal 

 gyri (Fig. 994). The diverging lateral stria obliquely courses along the antero- 

 lateral margin of the perforated space, but usually disappears as a distinct tract before 

 it can be traced to the uncus, its probable destination (page 1222). Occasionally the 

 lateral root is represented by two strands, an outer and an inner, the last one fading 

 away in the substance of the anterior perforated space. An additional intermedia^- 

 stria is sometimes recognizable for a short time before it too sinks into the anterior 

 perforated space. 



The olfactory trigone (trigonum olfactorium) is the three-sided slightly convex 

 area embraced by the two roots of the olfactory tract at the sides, and behind sepa- 

 rated from the anterior perforated space by a groove (sulcus parolfactorius posterior). 

 The triangular area seen on the inferior surface of the hemisphere (Fig. 993) is 

 really the under aspect of a more extensive pyramidal elevation, the tuberculum 

 olfactorium, which, however, lies in large part within the olfactory sulcus and is 

 therefore superficially not visible except at its base, the trigone. Retzius regards 

 this part of the hemisphere 



as a constant deep convo- FIG. 



lution, gyrus tuberis olfac- 

 torius, from which proceed 

 two ridges, gyrus olfacto- 

 rins medialis and later alis. 

 These bend respectively 

 inward and outward and 

 support the white strands of 

 nerve-fibres, the striae olfac- 

 torii, which are usually de- 

 scribed as the roots of the 

 olfactory tract. The tuber- 

 culum olfactorium contains 

 a considerable amount of 

 gray matter, which is a part 

 of the peripheral olfactory 

 cortex and, with other por- 

 tions of this sheet, shares 

 in the reception of axones 



from the mitral cells and in the origin of fibres passing to other parts of the 

 rhinencephalon. 



The parolfactory area, or field of Broca, lies as a small curved tract upon the 

 mesial surface of the hemisphere, just in front of and below the gyrus subcallosus 

 which extends from the rostrum to the corpus callosum (Fig. 994). The area 

 parolfactoria is bounded in front by the sulcus parolfactorius anterior and behind by 

 the sulcus parolfactorius posterior, and is connected in front with the superior frontal 

 gyrus, above with the callosal gyrus and below with the inner part of the trigonum 

 olfactorium, the mesial olfactory gyrus above mentioned. 



The anterior perforated space (substantia perforata anterior) is an irregularly 

 triangular area (Fig. 993) lying behind the trigonum olfactorium, from which it is 

 separated by the obliquely coursing sulcus parolfactorius posterior, and in front of 

 the optic commissure. Its inner part is narrow and extends as a point between the 

 mesial root of the olfactory tract and the lower end of the subcallosal gyrus. Its 

 broader outer part extends into the floor of the stem of the Sylvian tissure and 

 behind reaches the deeper part of the uncus and, more medially, the optic tract. 

 Its designation as perforated is justified by the large number of small oval apertures 

 for the transmission of perforating branches from the antero-mesial and antero- 

 lateral groups of the basal arteries. These openings, most numerous along the 

 front margin of the space, are disposed with some regularity in parallel tows and 



73 



Rostrum of 

 corpus calloi 



Septum lucidum 



Sulcus parolfactorius 



anterior 



Foramen of 

 Monro 



Anterior pillar 

 of fornix 

 Anterior 

 commissure 



Lamina cinerea 



parolfactc 



; posterior 



Gyrus subcallosus 



Portion 01 mesial surface of right hemisphere, showing gyrus subcallosus 

 and parolfactory area. 



