ANATOMICAL STBUCTUEE OF AJSTHEOPOID APES. 125 



of the orbit exceeds its height. In man, this seems 

 to arise from the exceptionally strong development 

 of the supra-orbital ridge. It is most probable 

 that in very young anthropoids the width of the 

 orbit exceeds its height.* Zuckerkandl goes on to 

 say that in anthropoids the height of the orbits is 

 greater than their width, and that this difference 

 increases with age. But this is not absolutely cor- 

 rect, for even in aged animals the proportions vary, 

 and the height and width of the orbits sometimes, 

 although rarely, remains the same. 



In comparing the vertebral column in men and 

 anthropoids, Eosenberg has sought to show in the 

 embryo, that the first sacral vertebra assumes the 

 form of a lumbar vertebra, and that in a later stage 

 of development it is enclosed by the ilia, and 

 anchylosed with the sacrum. The same author has 

 proposed a theory of the homologous or genetic 

 equivalents of the vertebrae, which we must now 

 consider. According to this theory, as Welcker has 

 observed, f the twentieth vertebra of an animal A is 

 homologous to the twentieth vertebra of an animal B, 

 the thirtieth vertebra of one animal to the thirtieth 

 of another, although in one case it may be a lum- 

 bar vertebra, in another a pelvic vertebra, and in 

 a third a coccygeal vertebra. The dorso-lumbar 

 vertebrae of the lower apes have, in the case of men, 

 their descendants, undergone a threefold metamor- 



* Zur Morjphologie des Gesichtsschddel, pp. 73, 85, 89 : Stuttgart, 

 1877. 



t Welcter on His und Braune, Archiv. fur Anatomie, 1881. 

 Rosenberg, Gegeubaur's Morphologisches Jahriuch, i. 172. 



