THE CHEIROPTERYGIUM, 509 



tions must be regarded as somewhat provisional, the actual interpretation 

 of various ontological processes being very uncertain. 



The forms investigated are Triton and Salamandra. We may remind 

 the reader that the hand of the Urodela has four digits, and the foot five, 

 the fifth digit being absent in the hand'. In Triton the proximal row of 

 carpal bones consists (using Gegenbaur's nomenclature) of (1) a radiale, and 

 (2 and 3) an intermedium and ulnare, partially united. The distal row is 

 formed of four carpals, of which the first often does not support the first 

 metacarpal ; while the second articulates with both the first and second 

 metacarpals. In the foot the proximal row of tarsals consists of a tibiale, 

 an intermedium and a fibulare. The distal row is formed of four tarsals, the 

 first, like that in the hand, often not articulating with the first metatarsal, 

 the second supporting the fii'st and second metatarsals ; and the fourth the 

 fourth and fifth metatarsals. 



The mode of development of the hand and foot is almost the same. The 

 most remarkable feature of development is the order of succession of the 

 digits. The two anterior (radial or tibial) are formed in the first instance, 

 and then the third, fourth and fifth in succession. 



As to the actual development of the skeleton Strasser, whose observa- 

 tions were made by means of sections, has arrived at the following results. 



The humerus with the radius and ulna, and the corresponding parts in 

 the hind limb, are the first parts to be differentiated in the continuous plate 

 of tissue from which the skeleton of the limb is formed. Somewhat later 

 a cartilaginous centre appears at the base of the first and second fingers 

 (which have already appeared as prominences at the end of the limb) in the 

 situation of the permanent second carpal of the distal row of carpals ; and 

 the process of chondrification spreads from this centre into the fingers and 

 into the remainder of the carpus. In this way a continuous carpal plate 

 of cartilage is established, which is on the one hand continuous with the 

 cartilage of the two metacarpals, and on the other with the radius and 

 ulna. 



In the cartilage of the carpus two special columns may be noticed, the 

 one on the radial side, most advanced in development, being continuous 

 with the radius ; the other less developed column on the side of the ulna 

 being continuous both with the ulna and with the radius. The ulna 

 and radius are not united with the humerus. 



In the further gi'owth the third and fourth digits, and in the foot the 

 fifth digit also, gradually spi'out out in succession from the ulnar side of the 

 continuous carpal plate. The caa-pal plate itself becomes segmented from 

 the radius and ulna, and divided ttp into the carpal bones. 



The original radial column is divided into three elements, a proximal 

 the radiale, a middle element the first carpal, and a distal the second carpal 

 already spoken of. The first carpal is thus situated between the basal 

 cartilage of the second digit and the radiale, and would therefore 

 appear to be the representative of a primitive middle row of 

 carpal bones, of which the centrale is also another represen- 

 tative. 



The centrale and intei'medium are the middle and proximal products of 

 the segmentation of the ulnar column of the primitive carpus, the distal 

 second carpal being common both to this column and to the radial column. 



1 This seems to me clearly to follow from Gotte and Strasser's observations. 



