.MORPHOLOGY OF THE BRAIX IX THE :MA:\r^rALIA. 341 



The Sylvian fissure is composed of Iwo separate sulci, pseudosylvian and suprasylvian, 

 :\s in L('it//tr; ])ut in this g-cniis tlicy l)Otli pursue the same direction and overhip so 

 slightly that it requires the closest examination to detect the lowei" end of the supra- 

 sylvian sulcus. As the result there is no ohvious depressed area, such as is found in 

 Lemur, hut its homologue is found in tlie anterior lip of the furrow in the region of the 

 lower end of the suprasylvian sulcus. Tiie lower })art of the pseudosylvian sulcus 

 is very shallow. 



Tlie up|i('r extremity of tlie supi-asylvian sulcus hecomes directly continuous 

 with the lateral sulcus, no suhmerged gyrus heing found to separate the two 

 elements. 



The lateral sulcus hends hackward, and then rinally curves inward in a manner exactly 

 analogous to that of Lemur J'ulcu.s. 



There is a small bracket-shaped sulcus J\ the concavity of wjiich faces the middle line. 



There is a sulcus about 7 mm. lung in front of and parallel to the suprasylvian 

 sulcus. Its ujiper part is bent backAvard so as to become almost horizontal. Thus the 

 sulcus may be regarded as consi.>ting of two limbs x and y. There is always a small 

 sulcus just above the orbital margin which we may regard as the sulcus coronalis. In 

 my type specimen this is so small as to be little else than a mere pit. 



There is a simple linear postsylvian sulcus. In my specimen (fig. 10) there are no 

 other sulci, nor even depressions to represent the sulci called a, b, c, and g in the brain 

 of Lemur. 



In the specimen of Nyctlcehm turdigradus [Siciiops javcuiicus, Illig.] described by 

 Flower (Trans. Zool. Soc. vol. v. pp. 103 et seq.) there are some slight differences. 

 Thus tlu; sulcus y appears to be absent and x is joined to the coronal sulcus, the 

 resultant furrow being called " iufero-frontal," which is the name Flower gives to the 

 coronal sulcus of Lemur. The sulcus /is represented as a long sagittal furrow, which is 

 called " supero-frontal " (]). 101). The writer remarks that the Sylvian fissure " makes 

 a slight change in direction, continuing to extend backwards " (p. 101), but thinks that 

 the lateral sulcus of the Lemur is absent. 



He represents a well-developed postlateral sidcus, such as is not found in my specimen. 

 Concerning this he says : — " A small sulcus running in a transverse direction on the 

 upper surface of the hemisphere, at the junction of the parietal and occipital lobes, 

 recalling the ' temporo-occipital ' (scisstire perpeJuUculaire exlerne) of the Quadrumana, 

 which iissure is, howevei-, Avanting in the smaller American Apes, as in Lemur " (p. 101). 

 We have seen above, however, that it sometimes occurs in Jjcmur, especially in the 

 species varius ; and even when absent as a separate element it is probably represented in 

 the " tail" of the lateral sulcus, both in Lemur and NijGlicebus. 



h\ the specimen in the College of Surgeons Museimi (fig. 11) the postlateral sulcus 

 is a separate element on the left hemisphere, but is merged in the lateral sulcus on the 

 right side. 



The upper end of the postsylvian sulcus bends forward, as it does in many Lemurs. 

 On the right hemispliere it presents an additional ramus parallel to the lateral sulcus. 

 In both hemispheres there is a little sulcus behind the upper end of the postsylvian 



