96 VERTEBRiE OF THE CROCODILE. 



Commencing with the trunk, the first and second ver- 

 tebrge of the neck are peculiarly modified in most air- 

 breathing vertebrata, and have ac; 

 ^^°' ^^' cordinglyreceived the special names, 



the one of " atlas," the other of " axis." 

 In comparative anatomy these be- 

 come arbitrary terms, the properties 

 being soon lost which suggested 

 those names to the human anato- 

 mist ; the " atlas," e. g.. has no power 



ATLAS/AXD AXIS VERTEBRAE ' 1 u i r 



OP THE CROCODILE. of Totatiou upou thc " axis," in the 

 crocodile, and it is only in the up- 

 right skeleton of man that the large globular head is 

 sustained upon the shoulder-like processes of the " atlas." 

 In the crocodile, these vertebrae are concealed by the pe- 

 culiarly prolonged angle of the lower jaw in the side view 

 of the skeleton (Fig. 18), and a figure of the two vertebrae 

 is therefore subjoined (Fig. 19). The pleurapophyses, ^9?, 

 are retained in both segments, as in all the other vertebrae 

 of the trunk. That of the atlas, ^jZ, a, is a simple slender 

 style, articulated by the head only, to the " hypapophysis," 

 ahy. The neurapophyses, n«, of the atlas retain their 

 primitive distinctness ; each rests in part upon the proper 

 body of the atlas, m, in part upon the hypapophysis. The 

 neural spine, ??5, a, is also here an independent part, and 

 rests upon the upper extremities of the neurapophyses. 

 It is broad and flat, and prepares us for the further me- 

 tamorphosis of the corresponding element in the cranial 

 vertebras. 



The centrum of the atlas, cof, called the " odontoid pro- 

 cess of the axis" in human anatomy, here supports the 

 abnormally-advanced rib of the axis vertebra, i^l^ x. I^he 

 proper centrum of the axis vertebra, co;, is the only one 



