476 The Phylogeny of the Palmar Musculature 
differentiation and association of the various layers has not proceeded 
to such a degree as to allow of an accurate application of such terms. 
I have already, in my previous paper (1903), shown that the use of the 
term flexor sublimis digitorum in reptilian myology is incorrect, and 
that the same is true of the terms interossei volares and interossei 
dorsales, these muscles as we recognize them in the mammalia not yet 
being differentiated, I shall show later on. The arrangement in layers 
in the amphibia and reptilia is the important matter for the present 
study and it is to this that I have endeavored to draw especial attention 
in my description. 
Ill. Tur Muscies oF THE MAMMALIAN HAND. 
In this chapter I propose to consider the muscles of the mammalian 
hand from the standpoint of their arrangement in layers, so as to obtain 
a general comparison with the condition occurring in the reptilia and 
amphibia, and, furthermore, I shall confine my remarks to what is 
found in the opossum (Didelphys virginiana), the cat and the mouse, 
reserving for a final chapter a detailed consideration of the muscles 
of the human hand. 
Cunningham in his admirable studies of the myology of the Chal- 
lenger marsupials (1878 and 1882) furnished a most important stand- 
point for the proper understanding of the fundamental plan of the 
mammalian hand musculature in recognizing its arrangement in a 
number of definite layers. He confines his attention to what he terms 
the “intrinsic” muscles of the hand, limiting that term so as to 
include only “those muscles which remain after the removal of the 
flexor and extensor tendons.” In this intrinsic musculature he recog- 
nizes three layers: (1) a palmar layer consisting of the adductors, (2) 
an intermediate layer and (3) a dorsal layer containing the dorsal inter- 
ossei and the abductores pollicis and minimi digiti. 
This conception seems to me to be faulty in three particulars. It 
may well serve as a plan for the mammalian hand muscles, if we limit 
our study to that group, but to obtain a correct understanding of the 
mammalian muscles we must formulate for them a fundamental plan 
which correlates them with the musculature of lower groups of verte- 
brates, and this cannot be satisfactorily accomplished if we limit the 
term “intrinsic” as Cunningham has done. For, as I endeavored to 
show in my earlier paper (1903), all the muscles of the hand are pri- 
marily “ intrinsic,” 7.e., confined to the limits of the hand, and not 
only must the muscles which Cunningham has discussed be included 
€ 
