66 BATRACHIAN- ILLUSTRATIONS OF LIMBS. 



fourth caudal vertebrae; short ossified pleurapopliyses 

 being developed from the ends of the diapophyses in the 

 first caudal to the vertebra dentata inclusive. 



By this instructive condition of the skeleton of the me- 

 nopome, we perceive at once that the haeraapophyses (26.), 

 H, are neither transverse processes, nor ribs bent down or 

 displaced, but are elements of vertebrae, as distinct as the 

 neur apophyses above. The neural arches are now articu- 

 lated together by well-developed zygapophyses with syno- 

 vial articulations, which are absent in the protopterus, as 

 in most fishes. 



In the protopterus, as in the squatina and some other 

 cartilaginous fishes, the neural arch of the atlas rests 

 upon a backward production of the basioccipital ; in the 

 batrachians it is confluent with its own proper centrum, 

 which developes two articular surfaces for the two oc- 

 cipital condyles. The haemal arch of the occipital seg- 

 ment, which is attached to its proper vertebra in the pro- 

 topterus (Fig. 32), A, 51, 52, as in osseous fishes, is 

 detached and displaced backwards in the batr-achians 

 (Fig. 33), 51, 52. In the completion of the hasmal arch 

 of the sacral vertebra in the menopome, by the enlarge- 

 ment of its transverse process^ (Fig. 11), D, and by its 

 pleurapophysis {ib.\ jjI, extended to join a haemapophysis 

 (lb.), H, below, we have the key to the essential nature of 

 the pelvis in all air-breathing animals. The progressive 

 development of the appendages of the scapular and pelvic 

 arches, which are to become the four limbs of air-breath- 

 ing vertebrates, should be traced from their condition in 

 the protopterus. Here (Fig. 32) they are reduced to a 

 single ray, which is soft and many -jointed. In the A^m- 

 phiuma didactyJa (Fig. 33) the ray ig ossified ; its first joint 

 {ih,\ 53, is long, its second {ib)^ 54, 55, js bifid, and a car- 



