xxxii PREFACE. 



The ' rudiments ' of parts and organs which are retained un- 

 developed, or do not acquire the state capable of acting, or ' per- 

 forming the function ' done by them in other species, are of two 

 kinds : one exhibits the totality of the organ in miniature, as, 

 e.g., lacteal glands and nipples of the male mammal; the other 

 is a part of an oi'gan, as, e.g., the few concealed caudal vertebrae 

 in the sloth, to which other vertebrae are added, with concomitant 

 growth, to make the organ perfect for its function, as in the tail 

 of the Megathere. Some rudiments show beginnings of parts 

 which rise to perfection in higher species of the existing series ; 

 others are remnants of organs that were fully developed and func- 

 tional in extinct species. Tiedemann's ' scrobiculus parvus in 

 loco cornu posterioris ' in the brain of Macacus, 1 and the part 

 which Vrolik believed himself entitled to regard as an indication 

 of the 'hippocampus minor' in the brain of Troglodytes? are 

 beginnings of structures which show their full development in 

 the human brain, and merit the nomenclature assigned to them 

 in anthropotomy. 



The filamentary limb of Protopterus (Vol. I. fig. 101, a), the 

 didactyle limb in Amphiuma {lb. b), the tridactyle homologue in 

 Proteus, are beginnings of organs which attain full functional de- 

 velopment in higher vertebrates. The styliform metacarpals and 

 metatarsals in Equus, on the other hand, are remnants of parts 

 of digits which were entire in Hipparion, and were functionally 

 developed in Palccotherium. 



Ruminants which habitually frequent heated arid plains or 

 deserts, as the giraffes and camels, e.g., have lost the digits (ii 

 and v, Vol. II. fig. 193, ox) that- add to the resistance of the hoof 

 on swampy ground, as in the bison, elk, and reindeer {lb. fig. 

 311). 



The visual organ degenerates in species inhabiting dark caves 

 or recesses {Amblyopsis (Vol. I. fig. 175), Heteropyg'd, Proteus, 



1 Icones cerebri Simiarum, fol. p. 14, fig. iii. 2. 



2 Vers], en Mededeel. cler Kon. Aknd.,xiii. 18(52, p. 7. 



