a correct St/stem of Muscular Homologies. 317 



third in the left foot ; of these the second, as indicated in the 

 foot, is evidently the missing third-toe muscle, while the first 

 may be the first-toe muscle, which is not otherwise developed. 

 If this be the case, the matter is still more clearly explicable in 

 accordance with the type proposed above. In I)asi/jyrocta the 

 same authors speak of a palmaris brevis muscle attached to the 

 palmar ossicle, but not connected with the digits, arising from 

 the first and fifth metacarpal bones. This muscle is a back- 

 ward prolongation of the type muscle, and evidently represents 

 the accessorius of the foot ; it is not present in the hare or 

 rabbit, but in the guineapig it is distinctly traceable. A small 

 muscle invests the flexor tendons still further forward in Agouti, 

 similar to the flexor brevis manus, but Avhich has no separate 

 digital insertion ; from the tendons themselves spring the 

 lumbricales, three in number, as in the cavy, guineapig, 

 rabbit, and hare : thus these three severed portions, if united, 

 would constitute an accurate and typical flexor muscle of this 

 series. In the human hand we find that this muscle, losing 

 its bony origin, is connected to the palmar fascia on the inner 

 side, and is known by the name of palmaris brevis, while its 

 digital slips remain as the lumbricales. I have seen this 

 muscle springing from the pisiform bone. Having thus traced 

 this flexor series through its various mutations, we see that, 

 despite its variability of form, it presents a constancy in its 

 presence, and is sometimes developed in a high degree of com- 

 plexity — for instance, in Nycticehus and the Lemuridse in 

 general, according to the illustrations of Messrs. Mivart and 

 Murie, and the text of Meckel, Vrolik, and others. We find 

 in these animals : — first, a doul^le set of ordinary lumbricales, 

 one on each side of each finger ; secondly, an accessory set, 

 likewise in duplicate ; and, lastly, a third series, passing from 

 the second to the third phalange of each digit : there are thus, 

 as Meckel states, twenty-four muscles in all of this lumbrical 

 group ; of these the first and second groups are only highly 

 differentiated slips of the flexor brevis manus, while the last 

 set may be continuations of the true dorsal interossei. 



The next groups of muscles in this segment are the inter- 

 ossei, palmar and dorsal, devoted to the purpose of lateralizing 

 the digits, the first series being flexors, and the second being ex- 

 tensors. In the typical limb, where each digit has a vital indi- 

 viduality of action, we should expect to find these muscles cha- 

 racteristically and perfectly developed ; but as in the limbs of 

 most vertebrates, when possessing four or five digits, only one 

 or at most two of them maintain this separateness of action, in 

 the intermediate segments consolidation of the metacarpals or 

 metatarsals interferes with independency of action ; still we find 



