GANOCEPHALA. 203 



the ossified part of that coracoid which it resembles in shape 

 and relative position. 



The perennibranchiate affinities oiArchegosaurus are shewn 

 as clearly by the scapular as by the hyoidean arch. The fore- 

 limb does not exceed half the length of the head. The humerus 

 (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 shews 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 Amjihiuma, the carpal segment 

 (56) in Archegosaurus. 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. Thus, in Archegosaurus, not 

 only is the small size of the fore limbs, but also their type of 

 structure, closely in accordance with that in the Perenni- 

 branchiata, as shewn in the tridactyle fore-limb of the Proteus 

 anguinus, of which a figure is added to that of the Archego- 

 saurus, in fig. 65. 



