174 THE ANATOMY OF VERTEBRATED ANIMALS. 



plates are in close relation with the pectoral arch, and 

 probably represent the interclavicle and clavicles. 



Minute bony plates cover the surface of the throat in a 

 small African Labyrinthodont, Micropholis. I have not met 

 with dermal ossicles in this position in other Labyrintho- 

 donts. But in Archegosaurus. PhoUdogaster, Urocordyhis, 

 Keraterpeton, Ophiderpeton, Ichthyerpeton, the integument be - 

 tween the thoracic plates and the pelvis presents regularly- 

 disposed rows of small elongated ossicles, which, for the 

 most part, converge from without, forwards and inwards, 

 towards the middle line. No trace of these appears upon 

 the tail, nor in any part of the dorsal region of the body, nor 

 on the limbs. 



The endoskeleton of the Amphibia is least complete in 

 Archegosaurus, where the centra of the vertebrae are rejore- 

 sented only by bony rings, the ribs and the neural arches 

 being well ossified. In other Labyrinthodonts of the same 

 (Carboniferous) epoch, however, such as Anthracosaurus, the 

 centra of the vertebrae are completely ossified biconcave 

 discs, very like the centra of the vertebrae of Ichthyosaurus. 



In the existing Proteidea, and in the Gymnophiona, the 

 vertebral centra are amphiccelous. In the Salamandridea 

 they are opisthoccelous. In Pipa and Bombinator they are 

 also opisthoccelous, but in other Batrachia they are, for the 

 most part, proecelous, but vary in different regions, some 

 being biconvex and some biconcave. 



The first vertebra, or atlas, presents two articiilar cups 

 to the condyles of the skuU, but there is no specially modi- 

 fied axis vertebra. 



The transverse processes may be simple, but in the Laby- 

 rinthodonts, and in the existing Salamanders, they are 

 divided into two processes — an upper tubercular, and a lower 

 capitular, process. When the transverse process is thus 

 divided, the proximal end of the rib is correspondingly split 

 into a capitular and a tubercular process. 



In the Gymnophiona, the Saurobatrachia, and the Laby- 

 ritdhodonta, the number of the vertebrae in the trunk is con- 

 siderable, and the members of the two latter groups have 



