Cerviad liiMx in Man. 93 



with which they are chissed, in liavin<r between the sternal rib and 

 the true rib an intermediate ril). The first ribs of monotremes are 

 more ri<;id than the tirst ribs of reptiles, but they are less riu'id thnn 

 the first ribs of mamnuils. In this connection it may Ije I'oiuted out 

 that in ruminants a diathrodial joint occurs between the ribs and 

 the sterna cartilages, whitli joint d(jes not upset the fixed neck type, 

 but it serves to illustrate the fact that impulses may determine the 

 formation of joints in parts of the body in which joints do not usually 

 occur. 



Neck curvature is practically absent from lizards and crocodiles : 

 it is slightly marked in the platypus, and more so in the echidna 5 

 it reaches its highest development in the mammals, such as llamas 

 and antelopes. The neck curves of birds do not occur in definite 

 places as they do in mammals, these definite neck curves being due to 

 the weight-carrying qualities and length of the fore-limbs, and also 

 to the length of the neck. The neck must be of sufficient length to 

 enable the animal to gather its food. 



The weight of the head suspended at the end of the neck has set up 

 impulses that have developed the ligamentum nmliae to conserve 

 tRe muscle energy of the muscles of the neck. The elastic ligament 

 always exerts its force in definite directions, and it is a prominent 

 factor in producing the definite neck curves of mammals. In n)an the 

 ligamentum nuchae is poorly developed, and his neck curv^es are 

 practically lost. 



When it is remembered that fish and snakes have cervical ribs, that 

 the crocodile has seven pairs of rib-stumps, that the Varnniif is 

 almost without rib tissue, and that quadrupedal ma'.umals are entirely 

 free from cervical ribs (except vestiges), it becomes apparent that neck 

 mobility, when associated with (juadrupedal progression, is hostile to 

 neck ribs. 



Xo quadrupedal mammal normally has cervical ril>s. No mammal 

 that habitually carries part of its body weight on the pectoral limbs 

 varies from seven neck bones. All mammalian cervical ribs and all 

 mammalian variations from seven cervical vertebrae, occur amongst 

 those mammals that have abandoned quadrupedal progression, such 

 as Bradijpus, Porpoise, Manatee, Diiyong and Man. 



Quadrupedal mammals remain true to neck type because they 

 perform those neck and limb functions which the mammals were 

 evolved to perform. Mammals that have abandoned quadrupedal 

 progression may show destruction of the fixed mammalian neck type, 

 but all such animals do not vary from fixed type. Those that are 

 variant have been submitted to impulses of a hostile nature ; great 

 stability of type occurs when the neck has to operate from a thorax 

 that has l^een made rigid by the impulses that are associated with 



