40 



VERTEBRATE SKELETON 



The vertebrae of Gymnophiona (fig. 46) are much like those of Perenni- 

 branchs in having no division of the intervertebral cartilage. They are relatively 



long, very numerous and each has a pair of trans- 

 verse processes on either side, the ventral side bear- 

 ing a spine directed forwards (probably united 

 haemapophyses), between the parapophyses. giving 

 additional strength to the column. No caudal 

 vertebrae occur. The short ribs are articulated to 

 the transverse processes and terminate differently 

 in the various genera. 



Fig. 46. — Vertebrae o f 

 Siphonops ( Wieder s h e i m , 

 '79)- 



Anura (figs. 40, 47) are characterized by the small number and 

 shortness of the vertebras, recent species, with few exceptions, having 

 eight presacrals and one sacral vertebrce, and a urostyle representing 

 the fused caudals, while the atlas is the sole cervical. 



In development the cartilages fuse early to a continuum in which 

 no intercentral parts are recognizable. An intervertebral cartilage 

 is formed between each two centra, divid- 

 ing so that the ball and socket joint is 

 usually procoelous, although a few genera 

 {Pipa, Bomhinator, etc.) are opisthocoelous. 

 Exceptionally, in the same individual some 

 centra are procoelous, some amphicoelous, 

 and some biconvex. Usually in all, the 

 eighth vertebra is amphicoelous, the sacrum 

 having a ball in front. In some Anura 

 {Pelohates, Bomhinator) the vertebras arise 

 wholly from the neural elements, the 

 haemal being greatly reduced or lacking, 

 so that the centra are epi- rather than 

 perichordal. 



The atlas, lacking transverse processes, 

 bears a pair of glenoid cavities, as in 



Urodeles, for articulation with the occipital condyles of the cranium. 

 The diapophyses of the other vertebrae are large, longest on the 

 sacrum where they articulate with the iliac bone. The sacrum 

 has two posterior tubercles for articulation with the urostyle 

 which is an elongate bone into which the spinal cord extends for a 

 short distance, giving off a pair of coccygeal nerves which pass out 

 through foramina in the sides of the bone. Coccyx and sacrum are 

 fused in Aglossa (fig. 47), and in Discoglossus (fig. 40) the urostyle 



Fig. 47. — Vertebral column 

 of Pipa (Hoffmann. '74). 

 s, sacrum; 11, urostyle. 



