134 THE VERTEBRATE SKELETON. 



premaxillae. There are no sternal ribs, and the sternum is 

 very intimately related to the pectoral girdle. There are no 

 obturator foramina. The limbs are as in the higher verte- 

 brata, divisible into upper arm, fore-arm, and manus (wrist 

 and hand), and into thigh, shin, and pes (ankle and foot) 

 respectively. The posterior limb is, as a rule, pentedactylate, 

 but in nearly every case the pollex is vestigial or absent. 



Order 1. URODELA 1 . 



The Urodela are elongated animals with a naked skin, a 

 persistent tail, and generally four short limbs. 



The vertebral centra are opisthocoelous or biconcave, and 

 there are numerous precaudal vertebrae. Portions of the 

 notochord commonly persist in the intervertebral spaces. In 

 the skull there is no sphenethmoid forming a ring encircling 

 the anterior end of the brain, its place being in many cases 

 partly taken by a pair of orbitosphenoids. There is no 

 quadra tojugal, and the quadrate is more or less ossified. The 

 mandible has a distinct splenial, and the articular is ossified. 



There is no definite tympanic cavity. The hyoid apparatus 

 is throughout life connected to the quadrate by ligament, and 

 a large basilingual plate does not occur. The ribs are short 

 structures with bifurcated proximal ends. In the pelvis the 

 pubis remains cartilaginous, and there is a bifid cartilaginous 

 epipubis. The bones of the fore-arm and shin remain distinct, 

 and the manus never has more than four digits. 



Suborder (1). ICHTHYOIDEA. 



The vertebrae are amphicoelous, but the notochord re- 

 mains but little constricted throughout the whole length of 

 the vertebral column. Three or four branchial arches nearly 

 always persist in the adult. The cartilages of the carpus 

 and tarsus remain unossified. 



1 See E. Wiedersheim, Morpkol. Jahrb. Bd. in. 1877, p. 459. 



