MOEPHOLOGT OF THE BEAIX ]\ THE r^EAMMALIA. 11 <) 



re. 



The an-angcment and beliaviour of the sulci ou tlie outer aspect of the heniisph( 

 closely follow those of the Ape, and especially of the lo\vlier Cehidie. There is the; 

 same peculiar form of suprasylviau sulcus merged ia the Sylvian fissure in both 

 Families. The lateral sulcus is closely similar, as in fact it is in all mammals, hut it 

 shows a peculiar tendency, which is exhibited in NycllcebuH in (he Lemurs and in 

 Chnjmlhrix, Xiictii)itheci(.'<, and JEycctes in the Cebidte, to become concurrent with \\\o 

 suprasylviau (Sylvio-intraparictal union), which is a striking instance of the Avidf; 

 separation of the Primates from all other mammals (in most of Ayhich the first stage of 

 this process, /. e. the pushing, as it were, of the suprasylviau sulcus on to the pseudo- 

 sylvian sulcus, has not begun, so that tlie further stage of pushing (he lateral sulcus into 

 tlie Sylvian complex is not even possible); at the same time it is a further testimony to 

 the affinity of the Lemurs and the Cel)idfG. 



So far as the other sulci — the coronal, the orbital, the diagonal (fronto-orbital), the 

 central rudiment, the postsylvian, and the postlateral — are concerned, there is tin; 

 closest identity between all of these in the Lemurs and such lowly Cebidu; as Cairdh,-i.i\ 

 the importance of which is again enhanced by the contrast affonU^d by the beJiaviour of 

 their respective representatives in other mammals. 



There is no sulcus, perhaps, more distinctive of the Primates than the noi-mally- 

 constituted central (Rolando's) sulcus. Such a sulcus (as a unit) is not found in any 

 other Order of mammals ; but there is a widespread tendency in the Lemurs — in 

 Terodicticus of the Lorisina>, in certain cases in FropUhecn.s, and in Cldroinijs — to the 

 development of this characteristic sulcus. 



The fronto-orbital sulcus, w'hich, like the paracalcarine, is absent in many New- World 

 Apes, is often as fully de\ eloped in the Lemurs {Lemur, PropUhecns, and Indris) a^ it is 

 in the larger Cercopithecidtc. And even if this furrow (as in the analogous case of the 

 paracalcarine) is represented among the other mammals (in the diagonal sulcus), it 

 it still important that a furrow which is not ju'esent in many New-World Apes j-hould 

 occasionally develop) in the Lemurs in the same situation and have the same form as tiie 

 fronto-orbital sulcus in the larger Apes. 



The degree of aflinity of one mammal to another is a purely relative matter, which it 

 is difficiilt to express adequately. But if we take all the features of neopallial sulci into 

 consideration, it can confidently be stated that, judged by the standard of the otlier 

 mammalian subdivisions, the ditTerences between the brain in the Lemurs and such 

 Primates as the Cebidfe ara ctn'tainly not worthy of being granted either Ordinal or 

 even Subordinal imjiortance. 



The differences between the brain in the Edentate Pamilies Myrmecophagidw, Dasy- 

 podid;e, and Bradyjiodida^ (which we recognize to be united by bonds of affinity) are 

 considerably greater than those m hich divide the Lemurs and Cebidte. Or, to adopt a 

 more certain or, at least, more genei-ally recognized scale of relationships, there is a 

 much closer resemblance between the brain in the Lemiu's and Apes than thei-e is 

 between those of the ^Eluroid and Arctoid Carnivores. 



So far as the neopallial furrows arc concerned, the Lemurs m.iglit be regarded as 

 inseparable from the Cebidte, if it were not for the fact that the other parts of the brain 

 exhibit-verv definite distinctive features. 



