PREFACE. xix 



Articles VJI.-IX. " Des os clu pied," ' l the frame of the hind 

 feet of Man, Ape, Lion, Seal, Elephant, &c., is shown to consist 

 of homologous bones. Nevertheless the great zootomist, in his 

 labour and character as zoologist, does not hesitate to define and 

 differentiate the ' foot,' the ' hand,' the ' paw,' the ' fin,' and the 

 ( hoof,' respectively : nor does he deem the demonstration of the 

 unity underlying the diversity to make the f man ' an f elephant ' 

 or a ' seal,' any more than it makes him a f dog ' or an ' ape ' ! 



The ' corpus callosum ' is defined as ' a horizontal mass of trans- 

 verse fibres covering the lateral ventricles, and exposed by divari- 

 cating the cerebral hemispheres.' If a group of mammals want 

 such commissural fibres, and another group possess them, the 

 classifier will avail himself of a well-defined term expressing such 

 difference, without prejudice to his reception of any homological 

 determination of the parts, or their rudiments, 2 in anatomical 

 works of the applier of the term. 



Only by ignoring such indication of the e rudiniental com- 

 mencement of the corpus callosum,' may a semblance of superior 

 knowledge be assumed by him who asserts, as an antagonistic 

 proposition to an affirmation of its absence as a zoological cha- 

 racter, that the Marsupialia, e.g., do possess the ( great com- 

 missure,' or ( corpus callosum.' 3 



So likewise with other well-defined parts of the human brain, 

 the homologues of which may not be traceable to the same extent 



QJ V 



down the mammalian series. KUHL, e.g., in Ateles Belzebutli* 

 TIEDEMAXN in the Macaque 5 and Orang, 6 VAN DER KOLK and 

 VROLIK in the Chimpanzee, 7 and myself in the Gorilla, 8 had 



1 Le9ons d'Anat. Comparee, vol. i. 1799. 



2 As given in the 'Philosophical Transactions' for 1837, p. 41. 



3 Proceedings of the Royal Society, No. 72, and March 23, 1865. 



4 Beitrage zur Zoologie tind vergleichenden Anatomic, 4to. 1820, zweite Abtheilung, 

 p. 70, Taf. vii. 



5 Icones cerebri Simiamm, fol. 1821, p. 14, fig. iii. 2. 



6 Treviranns, Zeitschrift fiir Physiologie, Bd. ii. S. 25, Taf. iv. 



7 Nieuwe Yerhandliugeu der erste Klasse van het Koningl. Nederlandsche Instituut. 

 Amsterdam, 1849. 



8 Fullerian Lectures on Physiology, Royal Institution (March 18, 1861); reported, 

 with copies of diagrams, in ' Athenpeum/ March 23rd, 1861, p. 395. 



a 2 



