The " Plathander" (Xenopus laevis). 
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ment can be furthered in two very effective ways : (1) shortening of the 
pre-sacral vertebral column, and (2) increasing the rigidity of the column. 
The first is effected in Xenopus by extending the sacral vertebra forwards 
to the fourth pectoral (since this vertebra has also a share in iliac articula- 
tion) while the second is effected by the interlocking, longitudinal ridges 
and furrows on the zygapophyses. The fore-limbs, as mentioned above, 
are only used in feeding, and locomotion is entirely a function of the 
strong hind-limbs. 
Fig. 2. — Dorsal view of skull. The nasals (N) lie dorsal to the fronto-parietals (FP). 
The Skull (Figs. 2 and 3). — If the Plathander is left in boiling water 
for a few minutes, the skin and other soft tissues can readily be removed 
and the component bones of the skull disarticulated. 
Boof of Cranium. — There is a very minute supraoccipital (SO) which 
remains cartilaginous ; the frontals and parietals of both sides have 
fused and the two lateral fronto-parietals, so formed, have also fused 
along the median line (FP in Fig. 2). The Ethmoid region remains 
cartilaginous (Eth in Fig. 2). 
Floor of Cranium. — In disarticulating the skull, one cannot separate 
the bones marked PS, OS, BS, and AS. Posterior to the bone BS 
