532 Mr. Owen on species of 



if present at all in the existing Batrachia, exist only as straight and short rudimen- 

 tary styles. Now the cause, or the essential condition of this defective state of the 

 costal apparatus in the existing Batrachia is well known to be their fish-like mode 

 of generation ; viz. the simultaneous development of their numerous ova, which 

 demands a capacity and produces a distention and dilatation of the abdomen in- 

 compatible with the presence of the bony hoops which encompass that cavity in 

 the reptiles that develope fewer ova, and mature them at successive intervals. 

 Hence, if the structure of the nasal cavity of the Labyrinthodon, as displayed in 

 two of the fossils here described, forbids the supposition that they breathed air 

 after the manner of Batrachians, we may infer a Saurian condition of a part of their 

 skeleton which has not yet been seen, and even gain considerable insight into the 

 generative economy of a race of reptiles peculiar to one of the most ancient periods 

 at which this order of vertebrate animals was called into existence. 



Vertebra.— Of the bones of the trunk there exists in the present collection only 

 a fragment of a vertebra referable to the Labyrinthodon pachygnathus (PI. XLV. figs. 

 1-4.). The fragment in question consists of the upper part of the body of a vertebra, 

 with the anchylosed neurapophyses, from which the transverse, the spinous and 

 the posterior oblique processes have been broken away. The length of this frag- 

 ment is two inches ; the breadth of the articular end of the body of the vertebra 

 one inch three lines ; the upper half of this surface is preserved at the posterior 

 part of the vertebra, showing that it is slightly concave, in which it deviates from 

 the vertebral system of existing Saurians and anourous Batrachians, but corre- 

 sponds with the vertebra of the Labyrinthodon leptognathus before described. 



The fractured surfaces for the transverse processes show them to have been broad 

 and thick at their origin ; they measure nine lines in antero-posterior diameter 

 and four lines in vertical extent. Below the transverse processes the body of the 

 vertebra is compressed and concave ; there is a small excavation at the anterior 

 part of the base of each transverse process. The spinal canal is five lines broad 

 and four lines high. The base of the spinous process is much contracted at the 

 middle of the neurapophysial arch, from which point it has been based upon two 

 distinct ridges, which thence diverge to the outer side of each of the anterior 

 oblique processes. The articular surface on each of these processes is flat, and 

 looks upwards and slightly inwards. 



The concavity of the posterior articular surface of the centrum is demonstrated, 

 and a like configuration of the anterior end may be safely inferred: thus, in the bicon- 

 cave character of the vertebra, its lateral compression and smooth surface, the thick- 

 ness of the transverse processes, and the size, shape and direction of the oblique pro- 

 cesses, a close generic resemblance is manifested between the present vertebral frag- 

 ment and the more perfect one of the Labyrinthodon leptognathus ; and the fissure at 



