Rhixexcephalox 91 



the olfactory tract is the endorhinal groove {sulcus endo- 

 rhinalis). At each side of the optic chiasma, the lateral 

 olfactory gyrus expands rather suddenly in a ventro-medial 

 direction, forming the large pyrijorm lobe {lobus piriformis, 

 lobus sphenoidalis) with a prominent medial eminence, the 

 uncus of human anatomy, and the fibres of the olfactory tract 

 are dispersed in this enlarged lobe. The related gray matter 

 medial to the lateral olfactory gyrus forms the anterior 

 olfactory lobe {intermediate olfactory nucleus), while the pyriform 

 lobe and the lateral olfactory gyrus make up the posterior 

 olfactory lobe. There appears to be no real structural difference 

 between the lateral olfactory gyrus and the pyriform lobe, 

 so that the latter term is sometimes applied to the whole 

 posterior olfactory lobe, though the two parts are said to 

 have different origins (Herrick). This region is separated 

 laterally from the neocortex by a groove, the rhinal fissure 

 or limbic fissure {sulcus rhinalis, fissura rhinica, fovea limbica), 

 while a slight depression, the incisura rhinica, bounds the 

 anterior part of the lobe medially (Pis. II., XIV. -XXIV.). 

 The anterior olfactory lobe is probably concerned particularly 

 with the "oral sense", which is simply correlated smell, 

 touch, taste, and muscle sensibility of the snout region, and 

 which is important in feeding reflexes. 



The cortex of the anterior olfactory lobe, or praepyriform cortex, 

 differs from the cortex of the pyriform lobe and the neocortex in being 

 thinner and in consisting of only three layers, the zonal or plexiform, 

 granular, and ganglionic layers {laminae zonalis, granularis, and ganglion- 

 aris). The granular layer of the praepyriform cortex is a dense band 

 of cells, which (except at its anterior and posterior extremities) forms a 

 series of longitudinal folds covering the ventral surface of the hemisphere 

 and extends at its medial edge to the ventral part of the septum. From 

 these folds of the granular layer, which serve to increase its area, small 

 groups of cells separate off as the islands of Calleja (ganglia olfactoria), 

 and certain special nuclei are distinguished in the medial part (nuclei of 

 the medial and lateral olfactory tracts). This large area with the cortical 

 folds and islands is usually called the tuherculum olfactorium, but includes 

 also the anterior perforated substance. Both of these are much reduced 



