624 



THE NEKVOUS SYSTEM. 



attached end of the peduncle is called the trigonum olfactorium. Immediately 

 behind the trigone a small obliquely placed ovoid area of gray matter, the 

 tuberculum olfactorium, can sometimes be detected in the human brain ; but in the 

 brains of most mammals with a greater development of the organs of smell this 

 swollen area is much more prominent and constant. In most human brains, 

 however, it is difficult to distinguish it from a much more extensive area, which is 

 situated behind it and to its lateral side, and is named the substantia perforata 

 anterior (Fig. 552). Along the anterior margin of this perforated substance there 

 can sometimes be detected a small, rounded, rope-like strand of gray matter, the 

 medial end of which passes into the trigonum olfactorium. This is the anterior 



Tuberculum olfactorium 

 Olfactory tract , | 

 Optic tract 



Substantia perforata anterior I 5 / 

 Stria olfactoria lateralis upon anterior | \ 



part of piriform area 

 Nucleus amygdal* (cut surface) 

 Piriform area (cut surface) 

 Limen insulae 



Optic nerve 



1 Optic chiasma 



i i Infundibulum 



Corpus mamillare 



Substantia perforata posterior 

 / Oculomotor nerve 



Internal capsule 





Optic radiation / / / 



Stria terminalis / /. / 



Caudate nucleus / / ' 



Lateral geniculate body ; ' 



Brachium colliculi superioris [ 

 Thalamus (pulvinar) 



Medial geniculate body i - 



Basis pedunculi cerebri 1 



Red nucleus 



/ Optic radiation 



/ / Caudate nucleus 

 / i 



; Stria terminalis 

 Radiatio tlialamo-temporalis (acoustic 

 radiation) passing from the medial 

 geniculate body into the anterior 

 transverse temporal gyrus 



Substantia nigra 



FIG. 552. PART OF THE VENTRAL SURFACE OF THE PROSENCEPHALON, SHOWING THE ATTACH- 

 MENT OF THE OLFACTORY TRACT. 



Olfactory area, dull yellow ; optic, blue ; motor fibres, red ; acoustic fibres, bright yellow. 



part of the area piriformis the stalk of the pear-shaped lobe and upon its surface 

 is placed a very well-defined narrow band of nerve-fibres, the stria olfactoria 

 lateralis, which is composed of axons of mitral cells (in the olfactory bulb) pro- 

 ceeding to the piriform area. Even when the anterior part of the piriform area 

 is not distinguishable, the stria lateralis is always a prominent feature. 



The piriform area extends transversely laterally in the deep valley between 

 the orbital and temporal regions of the hemisphere (fossa cerebri lateralis) : 

 becoming slightly broader, and reaching what is known as the insula (of which it 

 forms the limen insulse), it becomes sharply bent upon itself (Figs. 552, and 553, C) 

 It then passes medially and backwards, and emerges from the fossa as a broad 

 area upon the under surface of the temporal region (Fig. 553, C). This greatly j 

 expanded caudal extremity of the pear is the area piriformis in the strict senst j 

 of the term. 



