EXISTING ORGANISMS— ANATOMY 87 



already considered. The circulatory system is among the best to 

 demonstrate relationships, and has already been considered under 

 embryology. The nervous system is very evidently formed by 

 the modification of the same primitive parts in the various classes, 

 as is shown in the figure comparing the brain structure of 

 vertebrates (Fig. 60). In all systems there are evidences of struc- 

 tures having persisted beyond their period of usefulness in the 

 form of vestiges. These are especially interesting in man. 



Supernumerary Mammae. Wiedersheim records numerous in- 

 stances of the occurrence of supernumerary mammary glands. 

 These glands develop embryonically in a ventrolateral milk line, of 

 which all traces are obliterated except the normal adult mammae. 

 In such animals as dogs, cats and pigs which bear several young at 

 one time, these are several in number and lie in two rows indicat- 

 ing the position of the embryonic milk line, while in animals 

 whose young are usually limited to one or two at a birth a more 

 extreme localization limits the functional adult mammae to a 

 pectoral pair (Primates, etc.) or a pelvic pair or group (domestic 

 animals). In rare cases individuals, both male and female, have 

 in addition to the two normal pectoral teats of man a series of 

 additional rudimentarj^ teats in a row, as in lower mammals. In 

 females supernumerary mammae may be functional or mere ves- 

 tiges, while in males, since the teats are normally vestigial, the 

 same is true of others which may appear. Wiedersheim cites data, 

 dealing largely with soldiers, which show a surprisingly high per- 

 centage of polymasty. One observer whose records he uses re- 

 corded this condition in more than 5 per cent of cases. 



Persistent Hair. This peculiarity has also been recorded in 

 many individuals, such as Jeftichjeff, the "Russian Dog-Man" 

 and Julia Pastrana, a woman whose face was almost completely 

 covered by hair. These cases are probably due to the persistence 

 of the lanugo, a coat of hair which covers the body of the embryo 

 but is normally shed before birth and replaced by the restricted 

 hair of the adult. More significant evidences of relationship of 

 man with the lower animals are found in the resemblance of the 

 hair tracts on his body to those of quadrupeds. 



The Tail. While the tail in man is normally reduced to a series of 

 fused vertebrae, the os coccyx, completely enclosed within the 

 body, it too may develop occasionally as an external appendage. 

 Wiedersheim cautions against interpreting all such appendages as 



