+64 The Phylogeny of the Palmar Musculature 
I. THe PatMAr MUSCLES OF THE URODELOUS AMPHIBIA. 
The muscles of the Urodele hand are arranged in four layers, for 
which the terminology employed by Hisler (1895) is quite satisfactory. 
These layers are (1) a layer of flexores digitorum breves superficiales 
(Fig. 1, #. B.S.) arising from the palmar aponeurosis, (2) a layer of 
flexores digitorum breves medii (F. B. M.) also arising from the palmar 
aponeurosis, (3) a layer of flecores digilorum breves profundi (F. B. P.) 
arising from the carpals and metacarpals 
and (4) a layer of intermetacarpals (Im). 
A very considerable amount of similarity 
exists in the arrangement of the various 
digital slips derived from or composing 
each of these layers, although departures 
from the general plan occur in the mar- 
ginal portions of some of the layers. 
The flexores digitorum breves superfi- 
ciales.—The origin of these muscles in Am- 
blystoma is a curved lhne whose concavity 
is directed proximally and which is in the 
substance of the palmar aponeurosis, divid- 
ing this into a superficial and a deeper 
layer (Fig. 1, p. a.°s. and.p. a: d.). Whe 
muscular sheet arising from this line soon 
divides into portions corresponding to the 
digits, indeed, in some cases the portions 
are separate from their origin. The gen- 
eral plan for most of the portions may be 
briefly described as follows, according to 
TT ee ansverse: section” “what occurs im ‘the third digit, (liom 
EG: 
through the third and fourth 
metacarpals of Amblystoma tigri- This ot] divides 7 jing 
ii: Tee B fess toads wis portion divides into three ships, (1) a 
torum profundus; F. B. M., flexor 16 ~ thi arlies 
preva rodiden i BS Heese median one (F. 8.) which underlies the 
brevis superficialis; J. M., inter- a : > hal ‘ ar < = 
Tan canalie san pid eee ative tendinous prolongation of the palmar apo 
and fourth metacarpals; p. a. s. PQgTS jort « 7 ‘ > divides 
and p.@. @., superficial and deep  2cUTOSIS to the digit and eventually divides 
layersiof the palmar aponourosis” {9 he anserted into’ either) side sotgte 
fibro-cartilage of the metacarpo-phalangeal joint, and (2 and 3) 
two lateral slips (F. 8’.) which also insert into the sides of the 
metacarpo-phalangeal fibro-cartilage, uniting as they do so with the 
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a 
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lateral slips of the flexor digitorum brevis profundus. In the fourth 
digit the arrangement is essentially the same as in the third, but in the 
index and minimus only two slips are formed from each portion, the 
ulnar one being wanting in the index and the radial in the minimus. 
