THE SKELETON IN AMPHIBIA. PELVIC GIRDLE. 187 



further reduced. In Siren there are three or four, in Proteus 

 three, and in Amphiuma two or three digits in the manus. 



In Anura the pollex is represented only by a short 

 metacarpal. There are sometimes traces of a pre-pollex. 

 The carpus often has two centralia and the intermedium 

 is absent. 



In Labyrinthodontia the limbs are generally very simple 

 and resemble those of Urodela. In some forms, however, the 

 manus differs from that of all living Amphibia in possessing 

 five well-developed digits. 



PELVIC GIRDLE. 



The simplest Amphibian pelvis is that of some of the 

 Labyrinthodontia; thus in Mastodonsaurus it consists dorsally 

 of a short broad ilium placed vertically and attached to the 

 sacrum, and ventrally of a small pubis and of a large 

 ischium meeting its fellow in the middle line. In some 

 Labyrinthodonts the pubes as well as the ischia meet in 

 a ventral symphysis, and in many there are no obturator 

 foramina. In Siren, Gymnophiona and some Labyrinthodontia 

 the pelvic girdle and limbs are absent. 



In Urodela the ventral element of the pelvis on each side 

 forms a flat plate which meets its fellow of the opposite side. 

 The anterior part of the plate, representing the pubis, gene- 

 rally remains cartilaginous throughout life ; the posterior 

 part representing the ischium is in almost every case well 

 ossified. Attached to the anterior end of the pubes there is 

 an unpaired bifid cartilaginous structure, the epipubis. The 

 ilia are vertically placed. 



In most Anura the pelvis is peculiarly modified in corre- 

 lation with the habits of jumping. The long bone generally 

 called the ilium is placed horizontally and is attached at its 

 extreme anterior end to the sacrum. The ischium is ossified 

 and distinct. Ventrally in front of the ischium there is a 

 tract of unossified cartilage which is often regarded as the 



