620 THE CHEIROPTERYGIUM. 



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 first 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 observations 

 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 growth the third and fourth digits, and in the foot the fifth 

 digit also, gradually sprout out in succession from the ulnar side of the 

 continuous carpal plate. The carpal plate itself becomes segmented from the 

 radius and ulna, and divided up 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 carti- 

 lage 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 representative. 



The centrale and intermedium 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. 



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 corresponding 

 elements articulate respectively with the third digit, and with the fourth and 

 fifth digits. 



