286 DE. G. ELLIOT SMITH ON 



a mncli fuller and more accurate account of this peculiar brain than Pouchet has 

 provided. 



Max Weber has recently contributed an admirably illustrated account of the brain in 

 Manis, which is a most valuable supplement to Pouchet's imperfect work I have been 

 able to add slightly to Weber's account, and upon comparative grounds have interpreted 

 certain features in a somewhat different manner. 



The Ventral Surface of the Cerebrum. 



The most convenient landmark with which to begin the description of a brain for the 

 purposes of accurate comparison is probably the optic chiasma. The optic nerve, taking 

 its origin from the eye lying in the orbit, enters the cranium and extends toward the 

 base of the brain at the situation wliere the brain-stem joins the cerebral hemispheres. 

 In Orycferopiis * this point is situated about midway between the cephalic and caudal 

 extremities of the brain, or, to be exact, 52 mm. behind the apex of the hemisphere 

 (which is formed by the olfactory bulb), and 56 mm. in front of the place where the 

 medulla oblongata merges into the spinal cord. (These measurements, as all the 

 figures given in this memoir, refer to material which had been kept in alcohol for 

 jirolonged periods.) The optic nerves enter into relationship with the base of the brain 

 at this mid-point, and effect an intercrossing of fibres, the oj^dc chiasma, from each side 

 of which a rounded bundle of fibres, the oj^fic trad, arches laterally, and with a slight 

 inclination backward, to disappear (at a distance of 6-5 mm. from the mesial plane) 

 under an overlapping fold of cerebral cortex, which we shall subsequently recognize as 

 part of the j^yi'/form lobe. 



Por convenience of description we may regard the areas in front of the optic chiasma 

 as part of the cerebral hemisphere, and the parts behind it as the brain-stem. 



Immediately in front of the optic chiasma, on each side of the mesial plane, we find 

 a flat depressed quadrilateral area of about 8 mm. diameter. This is called by different 

 writers a variety of names, of which loctts 2ic>'foratus {ant lens) is as convenient as any. 

 As I shall not refer to any other ferforated space, I may omit the qualifying 

 adjective. In front of the perforated space we find a large oval area of grey substance, 

 which is slightly raised above the surrounding regions. This is the tnherculum olfuc- 

 toriuiii. Its major axis, which is sagittal, measures 18 mm., and its maximum breadth 

 13 mm. It is not confined to the ventral surface, but also extends on to the mesial 

 surface of the hemisphere, and there presents a fusiform outline below the precom- 

 missural area. The lateral border of the iuherculum olfactorium is clearly defined by a 

 furrow in which a A-ery compact strand of nerve-fibres, which constitutes the olfuctonj 

 trad, is found. In a fresh bi^ain the pure white colour of the latter would present 

 a marked contrast to the brownish-grey colour of the olfactory tubercle. TJie tradus 

 olj^actoriiis is situated upon the surface of a cortical area, which we shall call the anterior 

 l}art of ihe, jjyriform lobe. This jiart of the pyriform lobe is visible along the lateral 



* As practically nothing is known of the brain of Oryderopus, I describe it in some detail and point out the 

 features in other forms b}- contrast. 



