410 COMPARATIVE ANATOMY. 



§ 337. 



Among the Reptilia, the Chelonii resemble the anourous Am- 

 phibia ; there are no ribs in the cervical region of the vertebral 

 column, and it is doubtful whether the rib-like processes, which in 

 the trunk are connected with dermal bones, are not really transverse 

 processes. In the rest of the Reptilia, ribs are found on nearly all the 

 trunk vertebra). In the Saurii and Ophidii there are no ribs to the 

 atlas, and in the former there are none on the second cervical 

 vertebra either. In the Saurii, some of the ribs of the trunk are 

 connected with a sternum, and so make a great difference between 

 the various costiferous portions of the vertebral column ; in the 

 Ophidii, however, the ribs, from the second cervical vertebra as far 

 as the end of the trunk, have pretty much the same characters. They 

 are all characterised by their free articulation with the vertebral 

 column. 



In the Saurii and Crocodilini, each rib connected with the sternum 



Fig.230. Cervical and thoracic vertebra? of Crococlilus. c Ribs, c' Rib of the atlae. 



st Sternum. 



is always divided into several portions ; of these the upper, or ver- 

 tebral, is, as a rule, the only portion that is completely ossified. The 

 sternal end ordinarily remains cartilaginous, and but few ribs are 

 directly attached to the sternum. Not uufrequently a large number 

 are connected with a cartilaginous arch which is attached to its 

 hinder end. The more posterior cervical ribs, even, may be divided 

 into two segments, and so form an intermediate stage towards the 

 arrangement seen in the thoracic ribs. 



In Birds, the union between the rudimentary cervical ribs and 

 the vertebral column leads to most of them being completely fused 

 with it ; on the other hand, the hinder ones are less firmly connected, 

 and their mode of union is intermediate in character between that of 

 those in front of them, and of those thoracic ribs which reach to the 

 sternum. As in the Saurii, these latter are not numerous, and are 

 similarly divided into a vertebral and a sternal piece (os sterno- 

 costale). The vertebral pieces arc distinguished by backwardly 

 directed processes (processus uncinati), which are applied to the body 

 of the succeeding rib, and so increase the strength of the thorax. 

 This arrangement obtains also in some Saurii (Sphenodon) and in the 



