320 Dr. A. Macalister on the Formation of 



the poUex : these are differentiated fasciculi of the muscles 

 utilized for an important special purpose. 



The annularis or ring-finger has in man its palmar radial 

 muscle developed as the second palmar interosseus; and the 

 palmar ulnar, which arises generally from the unciform bone, 

 is shifted in its insertion, into the first phalanx of the little 

 finger, and constitutes the flexor brevis minimi digiti. For 

 the little finger the radial palmar muscle is developed in man 

 and the quadrumana as the third pahnar interosseus ; and as 

 such it exists in the armadillo. The palmar ulnar muscle is 

 developed into an abductor minimi digiti in the human hand : 

 this fact was first noticed in the case of the Ornithorhynchus^ 

 by Meckel ; but it will be found equally true in man, the cat, 

 and in such of the quadrumana as I have examined. 



The pedes of vertebrate animals, both mammalian and rep- 

 tilian, exhibit a corresponding series of muscles. Taking the 

 human foot as an example, we find for the tibial side of the 

 hallux a muscle, the abductor pollicis, or at least its calcanean 

 head, which is found in quadrmnana, many carnivora, and 

 marsupialia. On the fibular side a corresponding muscle, the 

 flexor brevis pollicis, occurs, a muscle whose single origin 

 indicates that it is not the complete representative of its syno- 

 nym in the hand. This muscle is absent in some monkeys, as 

 the mandril, but large in others, as Macacus. The second toe 

 has its tibial muscle circumstanced like its fellow of the manus, 

 and is thus modified into the adductor hallucis, a muscle which 

 is the undoubted representative of the deep head of the hand 

 flexor. From the fibular side of the second metatarsal we find 

 what should be the outer of the plantar muscles modified into 

 the first slip of the musculus transversus pedis, and crossing 

 the metatarsal bone to be inserted into the outer sesamoid bone 

 of the hallux ; the remainder of this transversus is made up of 

 the fibular interossei of the third, fourth, and part of the fifth 

 uniting and running transversely : its obvious manus repre- 

 sentative is the adductor pollicis, to which there is very often 

 an accessory fasciculus from the fourth metacarpal superadded, 

 as noticed by Huxley {loc. cit. p. 538). The tibial interosseus 

 of the third, fourth, and fifth toes remain in man unchanged, 

 as the first, second, and third plantar interossei respectively ; 

 of these the two last named exist in CercojntJiecus and Macacus, 

 but the first in these animals is either prolonged as a rudiment 

 of the transversus pedis or absent altogether. The flexor 

 brevis minimi digiti is made up of the remainder of the last 

 fibular muscle that is not required for the transversus. 



The plantar interossei having thus been accounted for in 

 man, it only remains to refer to their types the muscles in those 



