CROCODILIA. 13 



Crocodile,'' so far follows nature, and produces a parallel to his figure of a cervical 

 vertebra ; but the entire natural vertebra or segment includes the parts delineated 

 in outline in Cut 6, p. 5, Part I. In that figure is shown the semiossified bar It 

 which is interposed between the pleurapophysis pi and haemapophysis h in the 

 Crocodilia and some existing Lizards. The typical characters of the segment due to 

 the completion of both neural and haemal arches, is continued in some species of 

 Crocodilia to the sixteenth, in some {Crocodilus acutus) to the eighteenth vertebra. In 

 the Crocodilus acutus and the Alligator lucius, the haemapophysis of the eighth dorsal 

 rib (seventeenth segment from the head) joins that of the antecedent vertebra. The 

 pleurapophyses project freely outwards, and become ' floating ribs' in the eighteenth, 

 nineteenth, and twentieth vertebrae, in which they become rapidly shorter, and in the 

 last appear as mere appendages to the end of the long and broad diapophyses: 

 but the haemapophyses by no means disappear after the solution of their union 

 with their pleurapophyses ; they are essentially independent elements of the segment, 

 and they are continued, therefore, in pairs along the ventral surface of the abdomen 

 of the Crocodilia, as far as their modified homotypes the pubic bones. They are 

 more or less ossified, and are generally divided into two or three pieces. 



Another character afforded by the haemal arch is the more important in reference 

 to palaeontology, as it affects the centrum and neural arch of the vertebra as well as 

 the pleurapophysis ; and thus aids in the determination of the vertebra. The 

 parapophysis progressively ascends upon the side of the centrum in the two anterior 

 dorsal vertebrae, and disappears in the third, or, passing upon its neurapophysis, blends 

 with the base of the diapophysis. In this segment, therefore, the proximal end of the 

 rib ceases to be bifurcate, but is simply notched, the curtailed head being applied to 

 the end of the thickened anterior part of the transverse process, and the tubercle 

 abutting against its extremity ; in the five following dorsals the head and tubercle of 

 the rib progressively approximate and blend together, or the head disappears in the 

 tenth dorsal, in which the rib is simply attached to the end of the diapophysis. The 

 hypapophysis ceases to be developed after the third or fourth dorsal vertebrae. The 

 zvgapophyses become gradually more horizontal, the anterior ones looking more 

 directly upwards, the posterior ones downwards. 



The ' lumbar vertebrae' are those in which the diapophyses cease to support 

 moveable pleurapophyses, although they are elongated by the coalesced rudiments of 

 such which are distinct in the young Crocodilia. The development and persistent 

 individuality of more or fewer of these rudimental ribs determines the number of the 

 dorsal and lumbar vertebrae respectively, and exemplifies the purely artificial character 

 of the distinction. The number of vertebrae or segments between the skull and the 

 sacrum, in all the Crocodilia I have yet examined, is twenty-four. In the skeleton of 



* Ossemens Fossiles, 4to, torn, v, pt. ii. pi. iv, %. 4. 



