.510 THE CHEIROPTERYGIUM. 



The ulnar or fibular side of the carpus or tarsus becomes divided into a 

 proximal element the. ulnare or fibulare the ulnare remaining partially 

 united with the intermedium. There are also formed from this plate two 

 carpals to articulate with digits 3 and 4; while in the foot the corre- 

 sponding elements articulate respectively with the third digit, and with 

 the fourth and fifth digits. 



Gotte, whose observations were made in a somewhat different method 

 to those of Strasser, is at variance with him on several points. He finds 

 that the primitive skeleton of the limb consists of a basal portion, the 

 humerus, continued into a radial and an ulnar ray, which are respectively 

 prolonged into the two first digits. The two rays next coalesce at the 

 base of the fingers to form the carpus, and thus the division of the limb 

 into the brachium, antebrachium and manus is effected. 



The ulna, which is primitively prolonged into the second digit, is sub- 

 sequently separated from it and is prolonged into the third ; from the 

 side of the part of the carpus connecting the ulna with the third digit 

 the fourth digit is eventually budded out, and in the foot the fourth and 

 fifth digits arise from the corresponding region. Each of the three columns 

 connected respectively with the first, second, and third digits becomes 

 divided into three successive carpal bones, so that Gotte holds the skeleton 

 of the hand or foot to be formed of a proximal, a middle, and a distal row 

 of carpal bones each containing potentially three elements. The proximal 

 row is formed of the radiale, intermedium and ulnare; the middle row of 

 carpal 1, the centrale and carpal 4, and the distal of carpal 2 (consisting 

 according to Giitte of two coalesced elements) and carpal 3. 



The derivation of tliA Cheiropterygium from the Ichthyopterygium. All 

 anatomists are agreed that the limbs of the higher Vertebrata are derived 

 from those of Fishes, but the gulf between the two types of limbs is so 

 great that there is room for a very great diversity of opinion as to the 

 mode of evolution of the cheiropterygium. The most important speculations 

 on the subject are those of Gegenbaur and Huxley. 



Gegenbaur holds that the cheiropterygium is derived from a uniserial 

 piscine limb, and that it consists of a primitive stem, to which a series of 

 lateral rays are attached on one (the ulnar) side ; while Huxley holds that 

 the cheiropterygium is derived from a biserial piscine limb by " the length- 

 ening of the axial skeleton, accompanied by the removal of its distal 

 elements further away from the shoulder-girdle and by a diminution in the 

 number of the rays." 



Neither of these theories is founded upon ontology, and the only onto- 

 logical evidence we have which bears on this question is that above re- 

 corded with reference to the development of the Urodele limb. 



Without holding that this evidence can be considered as in any way 

 conclusive, its tendency would appear to me to be in favour of regarding 

 the cheiropterygium as derived from a uniserial type of fin. The humerus 

 or femur would appear to be the basipterygial bars (metapterygium), which 

 have become directed outwards instead of retaining their original position 

 parallel to the length of the body at the base of the fin. The anterior 

 (proximal) fin-rays and the pro- and mesopterygium must be supposed 

 to have become aborted, while the radius or ulna, and tibia or fibula are 

 two posterior fin-rays (probably each representing several coalesced rays 

 like the pro- and mesopterygium) which support at their distal extremities 

 more numerous fin-rays consisting of the rows of carpal and tarsal bones. 



