The appendicnlar muscles of Necturus macnlosus. 405 



The slips are thin and ribbon-like and taper slightly distally. 

 They are coincident with the entire extent of the metacarpals, and 

 insert into the bases of the four proximal phalanges, the insertions 

 being, in the case of digits II, III, and V, directly beneath the 

 similar ones of the median slips of the flexores breves superficiales. 



M. flexor interphalangeus digiti quarti (/?). This 

 minute slips appears in the fourth digit alone, and is evidently an 

 adaptation to the extra phalanx possessed by this digit, its purpose 

 being the supply of the extra Joint thus formed. It consists of a 

 few muscle fibers stretched across the flexor aspect of the articulation 

 between phalanges 1 and 2, and arises from the middle of the shaft 

 of the former and inserts into the base of the latter. It is often 

 divisible into two slips, placed side by side. 



That this muscle is in origin an extension of the flexor brevis pro- 

 fundus of this digit is rendered extremely probable, not only by its 

 appearance and general direction, but also by the occasional presence of 

 one or more fibers that connect the two and form a part of both. Such 

 a case, although not to be considered typical, has been selected as the one 

 figured, the usual condition being shown in the case of the corresponding 

 muscle of the hind limb (Figs. 34 and 35). 



Mm. carpometacarpales (ö, cd, ef, gh; those of the four 

 digits respectively). 



These form a third and still deeper layer of muscles between 

 carpus and metacarpus, lying beneath both sets of short flexors. 

 They are described by Eisler under the name of flexores breves 

 profundi, those designated here by that name being called the 

 medii; since, however, the carpo-metacarpales are not associated 

 with the palmar aponeurosis, and since they are in their use 

 adductors and abductors rather than. flexors, they can hardly be 

 treated as a part of the same System with the others. 



They arise without exception from the distal margin of the 

 carpalia and insert into the shafts of the several metacarpals by 

 oblique lines of Insertion. Typically there are two for each meta- 

 carpal, the one radial, the other ulnar, and as they are inserted 

 lateral to the median line of the digits they move the metacarpals 

 laterally and thus assist in spreading and approximating the digits, 

 a motion which, in this animal, is far more emphasized by the 

 difterentiation of the muscles than are flexion and extension, so 

 characteristic of the movements of higher animals. 



The details of the carpometacarpales in the separate digits 

 are as follows: 



