[Pkoc. Koy. Soc. Victoria, 25 (N.S.) Pt. I., ]912.] 



Art. VI. —The Occurrence and Development of Cerriral RiJ)S 

 la Mdii (1)1(1 some of the McDiimals tlmt liove ahdiuioned 

 Qi((i(lrupc(hd Pro<iresKi<)ii, 



By WALTER STAPLF.Y, M.D, D.V.Sc, M.R.C.V.S. 



(Lecturer in Anatomy and Suro-erv, Veterinary Schnnl. Melliourne 

 University). 



[Read 11th April, 1912]. 



Cervical ribs have acquired such a prominent place in modern sur- 

 gery that practical as well as scientific reasons demand that the 

 causes controlling- their formation should be investigated. The ob- 

 servations and deductions that are put forth in this paper are the 

 outcome of my enquiry into such causes, and tiiey foini an extension 

 of the abstract published in the Australian Medical Journal, August 

 19, 1911. 



The endeavour has been made to discover not only the influences 

 that cause the development of cervical ribs, but also the hostile 

 conditions that suppress rib growth and destroy rib structure. 



It Avill be shown that cervical ribs develop in the human neck 

 because the lungs have migrated towards, and encroached on, the 

 neck; and, from the conditii)ns associated with general rib develop- 

 ment, the deduction is drawn that cervical ribs form in the human 

 neck in response to impulses that are generated in the organism 

 which has been and is being excited by the presence of lung in the 

 neck. 



Classification of the Principal Stages in the Evolution 

 of Cervical Ribs. 



(1) The primary development of rib-structure in I ho neck-area. 



(2) The suppi'ession of necK rih-structurc. 



(3) The secondary development of cei'vical ribs. 



The primary development of rilis in the r.eck-area is illustrated by 

 the structure of fish. 



The suppression of cervical ribs can be studied in the following- 

 structures : — 



(a) The cervical ril)-slumps of crocodiles. 



(1)) Costal ))rt)cesses as they occur in the maumialian neck. 



