332 rUOF. G. ELLIOT SMITH OX THE 



Tanulndiui, Fclis, or Ovis. It is, however, liardly so plump as in any of these mammals, 

 and yet it is not nearly so small and attenuated as that of the Apes. In the 

 Hapalida', for example, the psalterium becomes so extremely reduced {dele Jonrn. of 

 Anat. and Phys. vol. xxxii. fig. 23, p. 51) tliat Beevor failel to find it even by 

 histological means. In tlie Lemurs its size is more considerable, and the chief 

 accunuilation of its fibres is never wholly separated from the splenium by an interval 

 devoid of commissural fibres, as liappens in 3Iidas {op. cit.) and the other Hapalidse. 



The septum lucidum, precommissural area, and anterior commissure present the usual 

 relations. 



Immediately behind the hi^^pocampal tubercle there is a very deep indentation, which 

 may possibly represent the caudal i-emnant of the rhinal fissure (fig. 5, a). It begins 

 close to (but without actually joining) tlie hippocampal fissure and passes obliquely 

 downward and backward. On the base of the lu'ain (fig. 4) it has all the appearance of 

 ioining the hippocampal fissure. Its extent and dii'ection vary considerably in different 

 brains of even the same species. In many cases (as, for instance, fig. 5) its dorsal lip 

 projects downward as a prominent rounded knob overlapping the deepened notch. 



Upon the mesial surface of the hemisphere there are a number of very stable and 

 constant sulci, and usually some otlier more variable furrovrs. 



By far the most important of these is a group of three, which may lie called the 

 calcarine complex. This is a triradiate pattern of sulci situated behind the splenium of 

 the corpus callosum ; the ventral limb maybe distinguished as " calcarine," the caudal 

 as " retrocalcarine," and the dorsal as " paracalcarine." 



Above and parallel to the corjius callosum there is a sulcus which will be called " inter- 

 calary " ; and in front of the genu there is generally a " genual sulcus " * of Krueg 

 (fig. 5). 



There is always an oblique sulcus placed below the retrocalcarine sulcus, which for the 

 present may be referred to simply as b. 



There is also a very oljlique sulcus (c) on the caudal margin of the hemisphere, midway 

 between the furrows a and h. 



•That portion of the mesial surface of the cerebral liemis2:)liere which lies below and 

 behind the corpus callosum is adapted to tlie shape of the contiguous structures. A deep 

 depression receives the optic thalami, a much smaller and shallower depression below and 

 behind the splenium is produced by the qnadrigeminal l)odies, and the broad flattened 

 area behind it is so moulded by contact with the upper surface of the cerebellum. 



The calcarine sulcus begins infei'iorly within the deep thalamic fossa just above the 

 sulcus a ; it ascends for about 3 mm. parallel to the hippocampal fissure and then 

 bending backward it crosses the rim of the thalamic fossa, traverses the mesencephalic 

 fossa, and ends in the cerebellar area, about 3 mm. behind the splenium. It attains a 

 depth of G mm. in its posterior part. 



In every brain (with only one exception) belonging to the genus Lemur which I have 

 examined the calcarine sulcus was continuous Avitli the retrocalcarine sulcus, the two 



* It is not altogelbcr certain whether it may not represent the " rostral" suleus. 



