50 ANATOMY OF VERTEBRATES. 



the hinder extremities — in the tailless order, especially the frogs. 

 In the seven vertebra) between the atlas and sacrum, two zyga- 

 pophyses looking upward are developed from the fore part, and 

 two looking downward from the back part of the neural arch ; 

 there is also a short spine. 



In the Toad (Bufo vulgaris) the number of trunk-vertebras, fig. 

 44, B, is the same as in the Frogs, but the diapophyses of the third 

 and fourth vertebras are relatively longer, those of the sacral 

 vertebra, s, relatively shorter, broader, and expanded so as to over- 

 lap the ilia, which are shorter and more arched. In Cystignathus 

 pachypus the sacral diapophyses are subcylindrical. In Pipa the 

 diapophyses of the second and third vertebras are of unusual 

 length, and support semi-ossified, short, flattened pleurapophyses. 

 The diapophyses of the four succeeding vertebras are short and 

 slender ; those of the sacrum are more expanded than in the toad, 

 and rest upon the anterior halves of the iliac bones. The coccy- 

 geal style shows, in most anourans, a simple anchylosed neural 

 canal, and also a hasmal canal, as at h, d, fig. 44. 



In the Ophiomorphs ( Ccecilia) the vertebras, besides being very 

 numerous, are biconcave. 



§ 19. Vertebral column of Ichthyopterygia. — In an extinct 

 order (Ichthyopterygia) of Dipnoal Reptiles, modified for marine 

 life, but breathing air, the trunk-vertebras were very numerous, 

 very short, and biconcave ; the centrums remained distinct from 

 the neural and hasmal arches, and were ligamentously, not sutur- 

 ally, united thereto. In the Ichthyosaurus communis, fig. 105, 

 there are about 140 vertebras ; in the anterior sixteen a short 

 parapophysis is developed from the side of the centrum, and 

 a diapophysis from the base of the neural arch ; but this soon 

 begins to project from the neurapophysial border of the centrum, 

 and then from the side of the centrum below that border. It 

 continues gradually to sink in position until, at about the fortieth 

 vertebra, it blends with the parapophysis, which alone continues 

 to represent a transverse process, as far as at about the eightieth 

 vertebra, 1 where it disappears and the succeeding centrums become 

 compressed, indicating the vertical position of the dermal tail-fin 

 which they supported. The atlas and axis centrums become 

 anchylosed by flat surfaces ; but each supports its own neural 

 arch. Between the lower part of the atlas and the occipital 

 condyle is a wedge-shaped hypapophysis, representing the part 

 called ' body of the atlas ' in anthropotomy : a similar bone is 



1 A dislocation or fracture commonly occurred at this part between the death and 

 final imbedding of the decomposing animal ; clxi. 



