374 PROF. K. YON BARDELEBETf Otf THE [Apr. 17, 



Ph., and in Pedetes there is a true nail (in some specimens only a 

 nail-like structure). 



The resemblance of Pp. and Ph. to a reduced thumb or great 

 toe is very striking (e.g. foot of Carnivora). 



If the first digit of the mammalian hand and foot had always 

 been lost as a true digit, and if we knew only mammals with four- 

 digits, then we might be in the same doubt about this reduced 

 structure — "prae-index" — as many of my colleagues are now about 

 my praspollex. 



The Pp. and Ph. are much better developed in lower mammals 

 than in higher ones — they are present and free in primitive types ; 

 they are lost or become united with their neighbours in higher or 

 more differentiated mammals, or they get the appearance of 

 " sesamoid bones." 



In lower mammals the Pp. may consist of two bones, in higher 

 there is always only one bone. 



The Pp. consists of at least two bones in Theriodesmus phyl- 

 archus, the position of that animal being not yet sufficiently 

 ascertained. Five years ago (P. Z. S. 1889) I supposed it to be a 

 Promammal, but, as Prof. Seeley kindly told me this March, there 

 is now evidence for this interesting animal being a true reptile. 



We must make a clear distinction betweeu the Jlssion of digits 

 which occurs in Cetacea (and Ichthyosauria perhaps) and the 

 existence of rudiments of digits. In Cetacea there is also a real 

 Pp., as Prof. Kiikenthal has shown. 



It may be that the Pp. and Ph. of many animals represent not 

 only an old (reduced) structure, but also a partly new one, and 

 that only the basis of the Pp. of Pedetes was inherited in those 

 species and that it gradually increased in size. 



There are many muscles in the mammalian hand and foot 

 which have to do with the Pp. and Ph. exclusively or nearly so. 

 When the Pp. and Ph. disappear or coalesce with other bones, 

 these muscles may also vanish or they may become united with 

 other muscles, or they may get inserted in those parts of bones 

 which have been originally free and more or less movable, as e.g. 

 Pp. and Ph. 



Concerning the nerve-supply of muscles I found that the 

 following muscles are provided with tivo nerves : — 



the flexor digitorum superficialis brevis manus ^ 



et pedis in 



the palmaris longus or flexor digitorum super- 1 , 



cialis longus ( 



the ulnaris internus (flexor postminimi) mammals, 



the flexor digitorum sublimis ) 



the flexor digitorum profundus, in all mammals. 



Concerning the homology of the true carpal and tarsal bones I 

 give here a table which, though it may be incomplete, I hope may 

 contain definite results : — 



