PLATANISTA. 465 



With somewhat of a direction parallel to the former, is another even more 

 highly contorted sulcus, which, beginning within the Sylvian fissure's anterior border, 

 has its termination quite on the opposite side, or right round to the base of the 

 temporal lobe (J). It likewise has many subsidiary sulci or spurs. This corresponds 

 with the fissure of Rolando or postparietal sulcus. 



Here, not below, but on the fore face of the anterior lobe of the cerebrum are 

 one or two sulci, which ascend and trend inwards towards the longitudinal fissure. 

 These may be regarded as representatives of orbitofrontal sulci. Quite on the 

 top of the brain and with parallel sinuosities, carried from frontoparietal to the 

 postoccipital lobe are several sulci separating the gyri, of which more shall be said 

 presently. 



As to the convolutions on this right hemisphere, apparently three orbital exist 

 and are, less or more, in continuity with the frontal gyri. An anteroparietal fold, 

 with several loops, follows the course already assigned to the correspondingly named 

 sulcus. Beneath this, and with the same kind of arched direction, is a long post- 

 parietal fold, which extends to behind the temporal lobe and outer postoccipital face. 

 Besides these, there seems to be a marginal gyrus ghding the fissure of Sylvius, and 

 the loops and lobule of which, about the middle of the Sylvian cleft, may in part 

 answer to the so-called central lobe or insula (island of E,eil), although here cer- 

 tainly freely exposed. Of temporal gyri there are a few, those of the supra- 

 temporal region at least having, in the main, a perpendicular and not a horizontal 

 direction. 



On the vertex, besides a portion of the gyrus bounding the longitudinal fissure, 

 that knowu as marginal, there are at least three broad elongated folds, placed 

 parallel to each other and extending from the suprafrontal to the postoccipital lobe. 

 Secondary longitudinal furrows occur within these, giving them an insular or looped 

 character, wriggling of the folds being most frequent at the occipital region. When 

 in the fresh condition, doubtless, subsidiary cross and obHque sulci give a more varied 

 aspect to this area. 



On the left hemisphere neither gyri nor sulci quite agree with what has been 

 described as occurring on the right half. Those longitudinal parieto-occipital folds 

 just spoken of present a modified pattern. The same holds good with the orbital 

 frontal, antero and post parietal and other gyri mentioned. Still, the main features 

 and general pattern have a certain likeness, the departures being in the secondary 

 turns and indentations. 



It is to be remembered that in the sketches, (PI. XXX,) some of these last are 

 not represented, and hence a smoother appearance is given than in reality the 

 brain possessed. 



I may sum up this much of the cerebral anatomy by stating that, so far as the 

 convolutions and sulci are concerned, this species of dolphin has a brain of a con- 

 siderably simpler type than in the porpoise or common dolphin, tending perhaps to 

 some of the Carnivora, though in such a slight degree as still to impress it with all 

 the attributes of the complex convoluted cerebrum of the Cetacea. 



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