126 



ANATOMY OF VERTEBRATES. 



Ill 



thrix, fig. 109) the sylvian fissure, 5, and fold, e, are directed 

 more obliquely from above and behind, downward and forward, 

 than in the Aye-aye, ib., and most Lemuridas : this character 

 appears to be due to the preponderating growth of the frontal 

 lobes, and becomes more marked as the Quadrumana rise in the 

 scale. We next find that each hemisphere is divided into an 

 anterior, middle, and posterior tract or region by two deep and 

 extensive fissures, 12 and 13, Macacus, fig. 109, and Cebus, fig. 116, 

 which, from their respective correspondence in position with the 

 coronal and lambdoidal sutures, bear the same names. 



In Cebus the sylvian fissure, fig. 116, 5, is overarched by a 

 subangular one defining the fold, g ; from 

 the angle a fissure, 13, extends to the inter- 

 hemispheral one, and is continued deeply 

 down the inner or mesial surface. Out- 

 wardly the lambdoidal fissure, 13, defines 

 and undermines a posterior part of the hemi- 

 sphere, by raising which the continuation of 

 the postsylvian fold,^ may be traced beneath 

 it. The chief difference between the cata- 

 rhine and lemurine hemispheres, at the inner 

 surface, is the superaddition and interposition 

 of the entolambdoidal fissure, 13', between 

 the post-hippocampal, V, and marginal or 

 super-callosal,7',fig. 117; the entolambdoidal 

 being sometimes continued into the post- 

 hippocampal fissure, as in fig. 118, 13' — 4'. 

 The almost transverse fissure, fig. 116, 12, di- 

 vides the large anterior from the middle lobes. 

 In the latter, however, may be recognised the 

 short tract, /, m, combining the * medial ' and 

 6 medilateral ' folds, but more transversely disposed than in Carni- 

 vora\ pushed out, as it were, by the backward growth of the 

 anterior lobe. Secondary fissures there indicate frontal, n, mid- 

 frontal, n" ', and superfrontal, n', folds. One or two longitudinal 

 occipital fissures mark out corresponding folds, q" ', q f/ '. The ecto- 

 rhinal fissure, fig. 111,2, sinking into the sylvian one, 5, may have a 

 continuation in the anteroposterior fissure, ib. 2', which divides the 

 ( natiform protuberance' into a medial or basirhinal, b, and a lateral 

 moiety, f. In most Catarhines the coronal fissure, 12, figs. 114, 

 116, extends, from within, more obliquely forward and outward; 

 the homologues of the platyrhine fissures and folds are clearly 

 seen, as marked by the figures and letters in Macacus and Cebus, 



Under surface of cerebral hemi- 

 sphere, Macacus. 



