70 PROFESSOR OWEN ON THE 



extent of this cancellous structure at the sides of the cranial cavity may be known by 

 the ratio of the breadth of that cavity to the breadth of the cranium, which is 3 inches 

 and 8 lines at the broadest part of the brain, viz. the prosencephalon. It would seem, 

 at first sio-ht, as if the poorly developed brain of the Dodo had needed, on some account, 

 unusual protection ; but the true explanation rests on the size, weight, and power of the 

 bill, and the concomitant necessity for adequate extent of attachment of the facial to the 

 cranial part of the skull, and of the muscles from the trunk destined to sustain and wield 

 the long and heavy-beaked head. The cerebrum of the Dodo does not greatly, and by no 

 means proportionally, exceed the size of that part of the brain in the Crown-pigeons 

 (Goura). If the great Ground-dove of the Mauritius gradually gained bulk in the 

 long course of successive generations in that uninhabited thickly-wooded island, and, 

 exempt from the attacks of any enemy, with food enough scattered over the ground, 

 ceased to exert the wings to raise the heavy trunk, then, on Lamarck's principle, the 

 disused members would atrophy, while the hind limbs, through the increased exercise 

 by habitual motion on land, with increasing weight to support, would hypertrophy. 



In the long course of generations subject to this slow rate of change, there would be 

 nothing in the contemporaneous condition of the Mauritian fauna to alarm or in any 

 way to put the Dodo to its wits ; being, like other Pigeons, monogamous, the excite- 

 ment, even, of a seasonal or prenuptial combat, might, as in them, be wanting : we may 

 well suppose the bird to go on feeding and breeding in a lazy, stupid fashion, without 

 caU or stimulus to any growth of cerebrum proportionate to the gradually accruing in- 

 crement of the bulk of the body. Whatever part of the brain was concerned in regu- 

 lating or controlling muscular actions, might, indeed, be expected to show some concur- 

 rent rate of increase with the growing mass of the voluntary contractile fibres ; and the 

 size of the cerebellar division (PI. XXIII. fig. 1, n o) of the cranial cavity accords with 

 the generally accepted physiology of the superincumbent mass of the epencephalon. 

 The lateral depression at the fore and under part of the side of the postcerebral division 

 of the cranial cavity indicates that the optic lobes, like the eyes, remained almost 

 stationary during the progressive acquisition of the bulk that distinguishes the Dodo 

 from the largest existing Doves. 



The proportions of Didus, Pezophaps, Casuarius, Rhea, Dromaius, Sfruthio, Aptornis, 

 Cnemiornis, Palaptevyx, yEpyornis, Dinorms, &c. among terrestrial birds, of Notornis 

 among the lake-haunting Coots, and of Aptenodytes and AJca impennis among sea- 

 birds, point to the disuse of wings in flight as the main condition of increase of size in 

 species of birds — the next condition being absence of lethal enemies during the years 

 requisite for such course and rate of growth. 



Let foes arise from whom a power of flight is the main condition of escape, and the 

 wingless giants of the feathered class soon succumb. Among the genera above-cited, 

 Aptornis, Cnemiornis, ^pyornis, Palapteryx, Dinornis, Didus, and Pezophaps, with the 

 largest of the Auks, have thus passed away, while Notornis and Apteryx are on the 



