CHAPTER IV. 

 MALFORMATIONS. 



DEFINITION. 

 ETIOLOGY. 



I nlniisic ( licrcdily.) 



E.vtriiisit. 



I'i'CSSlll'C. 



.-l)iiniotic .IJIicsion. 

 7i.vfi\i\ni't' Motion. 

 'Jdiinlri'loii. 

 CL.-lSSP-S. 

 Sini/lc. 



Result of Arrested DeTelopetiient. 

 Result of E.veessi-ee I h'Telof^eiiieut. 

 Result of Transposed I'isecral Orguas. 

 Result of Pcrsisleiit Tuelal Struetnrcs. 

 Result of Mixed Se.vuol Organs. 

 Double or .Multiple. 

 Syinmetrieul Puflieities- 

 Coiiiplete ( twins) . 

 I iieoniplete {double monster). 

 .Isvninietrieal LIuflieitles. 

 .Multiple. 



DuriiTL;- the emlir^-cinic stage of intra-nterine life the special- 

 ized tissues and (irnans arc furmed. The foetal period is the time 

 durint;' which the structures formed in the embryonic sta,a;e tjrow 

 and develiip. At 1)irth the \-ount;;- nf a gi\'cn species are of a 

 definite shape, contour and type ; the form or type which is most 

 common is accepted as normal; and deviations from the normal 

 are desia:nated malfi irmatii )ns, anomalies or developmental 

 errors. Alan\- new strains and breeds of stock have been the 

 result of developmental err(.)rs becoming a fixed peculiarity. 

 Thus the i)olled cattle, the Boston bull-dog, the ^Mexican (hair- 

 Jess) dog, and the five toed chicken had their origin. 



Etiology. — Malformations mav be brought about by pre- 

 existing influences in the maternal cells, (internal or intrinsic 

 causes), or from external influences (external or extrinsic 

 causes). 



hifcnial or Intrinsic Causes. — Internal causes are inherited 

 peculiarities, i e., heredity and atavismal influences. These are 

 probably not the usual causes of malformation in domestic animals 

 for malformed individuals are rarely used for breeding purposes. 



External or Extrinsic Causes of malformations are pressure, 

 amniotic adhesions, excessive motion, insufficient or abnormal nutri- 



9; 



