546 



REPTILIA. 



part of the body, which is here of extraordinary length and great 

 flexibility, into a powerful instrument of propulsion. 



(596.) The transverse processes of the cervical vertebrae are re- 

 markably large, and so extended that they materially interfere 

 with the lateral movements of the neck ; an arrangement evidently 

 designed to afford a sufficient extent of insertion for the powerful 

 muscles of the cervical region. 



(597.) The thorax is com- Fi s- 245. 



posed of a Sternum and two 

 sets of ribs ; one set being ar- 

 ticulated with the transverse 

 processes of the dorsal verte- 

 brae, and hence called dorsal 

 ribs; while the others, being 

 fixed to the sides of the ster- 

 num, are named sternal ribs : 

 the contiguous extremities of 

 the dorsal and sternal ribs are, 

 moreover, united by inter- 

 vening cartilages, which, as 

 they are generally more or 

 less perfectly ossified in the 

 adult Crocodile, might almost 

 be regarded as additional ele- 

 ments of the thorax. 



The posterior dorsal ribs 

 are far less perfectly deve- 

 loped than those situated 

 more anteriorly; and it is 

 not a little interesting to 

 observe how gradually, even 

 in the same skeleton, the 

 transition is effected from 

 the simple condition already 

 noticed in the ribs of fishes, 

 in which each rib is merely 

 appended to the extremity of 

 the transverse process of a ver- 

 tebra, to ribs perfectly adapt- 

 ed to enter into the compo- 

 sition of a true thoracic 



