Cervlcul HIb'S in M<in. 87 



It seeins a process of narrow roa«oiiiii'_; wliiili admits the orij^in 

 of new sjjecies, but refuses to admit that new structures nuiy be 

 evolyed. Tlie denial of the apjK-arance of new struetures seems to be 

 tlie basis of the theory of atavism. 



Where ribs develop in site.< that have been previously occupied 

 by vestipes of extinct ribs, new ril)-forniii)g impulses have arisen 

 which arc of a different character to those impulses that have sup- 

 pressed ii>-ck ribs and formed rib-vesti^es, or to those that have 

 broujflit about the extinction of rib. 



Daiwin did not fully urasj) the relationship ihat exists between 

 or<::ans. structures and >pe;-ies. It is apparent that structures and 

 organs form the parts of the species ; and it follows that that which 

 applies to the whole nuist ajiply to the part. Species are admitted 

 to suffer extinction through hostile influences, and therefore it must 

 also be admitted that structures and organs may likewise suffer 

 extinction by the same means. 



Bland-Button wrote: — "Much that is fancifid and speculative is 

 mixed uj) with the subject of atavism." and a study of neck ribs 

 compels the endorseujent of this remark, for it is a fanciful idea 

 that regards mamnuilian cervical ribs as atavistic to the ribs in the 

 neck area of fish. 



Mammalian cervical ribs develop in association with respiration, 

 tish ribs are unassociated with lung, therefore mamnuilian neck ribs 

 and ribs in the neck-area of tish are not teleologically related, for 

 they are each utilised for a ditt'erent purpose. It will be shown that 

 cervical ribs are late developments in the mammalian neck, which 

 developnu^nt is due to the impulses that are occasioned by the en- 

 croachment of lung into the neck. 



The costo-transverse foramen is absent from the seventh vertebra 

 in most tpuidrupedal mannnals that have well defined neck curves ; 

 j'.nd usually associated with the alisence of this foramen is the lack 

 of costal processes. The absence of costal processes from this bone 

 would appear to be determined by the fact that their presence would 

 hamper the range of what in quadrupedal aniujals is an extensive neck 

 movement occurring in this position. The seventh neck bone of such 

 animals has been submitted to extinction of its rib vestiges by the 

 hostile effect of neck Hexion upon a thoracic base that has been made 

 firm by the lateral pressure of the weight of the body. Occasionally 

 in true quadrupeds, the costal processes on the seventh cervical ver- 

 tebra are not suppressed oi! both sides. We have found this abnor- 

 mality in the racehorse " Traquair," and Dr. Dodd, of the Sydney 

 University, writes me that he also has a specimen of the same ab- 

 normality, that is, the costal process of the sixth neck bone is sup- 

 pressed on the same side as it is developed on the seventh. Sisson, 



