ON THE STRUCTURE OP THE LAByRlNTIIODONTS. 243 



merus) are very similar in form and present no uncommon difference of size*. 

 The hinder limb is larger and stronger than the other, as is usual with qua- 

 druped vertebrates. On the whole the structure and proportions of the ex- 

 tremities of Labyrinthodonts are similar to those of urodele Amphibia, and 

 indicate low-bodied aquatic animals. 



It is wcU known that the examination of the bones found in the Keuper 

 of Leamington and Warwick, together with a comparison of the footprints 

 named Oheirotherium, led Professor Owen to the behef that Lahi/rintJioclo)i 

 exhibited a striking disproportion between the fore and hind limbs. This 

 view accords well with the opinion that the Labyrinthodonts were anurous 

 Batrachia. But such a disproportion implies more than a near affinity with 

 the Batrachia : it is in this class (Amphibia) a mechanical provision for 

 activity in leaping ; and the inference from Professor Owen's hypothesis 

 would be that the Triassic Labyrintliodonts at least had in some measure the 

 habits of the frog. The supposition will not stand a moment's consideration. 

 That a Lahyr'intlwdon, with its greatly expanded and prolonged head could 

 have leaped a yard without a severe shock is improbable. But if we suppose 

 that it possessed the thoracic jilatcs and the loosely articulated shoidder- 

 girdle of other Triassic Labyrinthodonts, and if, with Professor Owen, we 

 interpret the structure of its extremities according to the Cheirotherian foot- 

 prints, the difficulty is greatly increased. The Labyrintlwdon would be a 

 leaping animal of gigantic size, weighted with i^rotective scutes, having little- 

 expanded toes, and not provided, to our knowledge, with a single one of 

 tliose special provisions which enable large animals to leap great distances 

 with safety. 



Wo one will explain the assumed disproportion of fore and hind limbs as 

 indicative of peculiar browsing or climbing propensities, such as those attri- 

 buted to Iguanodon or Hadrosaurits. The aquatic and predatory character 

 of the Labyrinthodonts is well established. 



Since the hypothesis under discussion involves such difficulties, it wiU be 

 desirable to reexamine the ground upon which it rests. 



Professor Owen's position is this : — Anisojms scutidatns, a presumed 

 Labyrinthodont, has a hind limb at least twice as large as the fore limb. 



An ilium and head of femur, presumed to belong to Lahyrinthodon 

 2''ac7iygnai7n(s, are greatly larger in proportion than a humerus referred to 

 the same species. 



In some Cheirotherian (presumed Labyrinthodont) footprints the tracks of 

 one foot are much larger than those of the other. 



The species of Labyrintlwdon differ considerably in size, as also do the 

 footprints of Cheirotheiium. 



It is hardly necessary to diseuss.the distinctness of the species of Labyrin- 

 tliodon or of Cheirotheriiim. The whole weight of the argument rests upon 

 the suppositions that (!) the bones named Anisopus scutidatus, (2) the ilium 

 and femur found at Warwick, (3) the humerus found separately at the same 

 place, (4) the footprints named Cheirothcrium, belong to Labyrinthodonts — 

 and, further, that the ilium and humerus found at different times in the same 

 quarry belong to the same individual, or to individuals of the same si^ecies 

 and age. 



Iliis chain of suppositions has not been strengthened by the further cvi- 



* There is no conclusive evidence that Anisopus is labyrinthodont. The rhomboidal 

 sculptured scute attached to the slab containing this specimen might seem confirmatory of 

 Prof. Owen's determination ; but, besides the Crocodilia, the Scelidosuuridx had dcru.al 

 armour. 



