OAXOCEPIIAL.Y 181 



(53) is a short thick bone, slightly constricted at the middle, 

 expanded and rounded at both ends, the proximal one being the 

 largest. For some time the bone is hollow and open at each 

 end ; when ossification finally closes the terminal apertures, 

 it shows that the ends were connected to the coracoid and to 

 the fore-arm by interposed ligamentous matter, — not, as in true 

 Saurians, by a synovial joint. Of the two bones of the fore- 

 arm the ulna is a little longer and larger than the radius (54). 

 Both bones present the simplest primitive form, gently con- 

 stricted in the middle, with the proximal ends a little concave, 

 the distal ones a little convex. The space between the anti- 

 brachium and the metacarpus plainly bespeaks the mass of 

 cartilage representing, as in Ampliiuma, the carpal segment 

 (56) in Arclicgosaurus. No trace of a carpal bone is found 

 save in the largest and oldest examples, in which five or six 

 small roundish ossicles are aggregated near the ulnar side of 

 the carpus. Four digits are present ; and considering the 

 pollex to be, as usual, wanting, the second digit answering to 

 the medius of pentadactyle feet, is the largest, and includes at 

 least four phalanges (58) ; these, with the metacarpals (57), are 

 long, slender, terminally expanded, and truncate. They obvi- 

 ously supported a longish, narrow, pointed paddle. The outer- 

 most or little finger was the shortest, and has the shortest 

 metacarpal and first phalanx. 



It is true that in Mystriosaurus the fore limbs are relatively 

 almost as short as in Arclicgosaurus ; and the oolitic crocodile 

 recalls the arrest of development of the same limbs in the 

 marsupial Potoroos ; but in Arclicgosaurus, not only is the 

 small size of the fore limbs, but also their type of structure, 

 especially that of their scapular arch, closely in accordance 

 with that in the Pcrennibranchiata, as shown in the tridactyle 

 fore-limb of the Proteus anguinus, of which a figure is added 

 to that of the Arclicgosaurus in fig. 65. 



The ilium (62), like the scapula, is expanded at its articular 



