J. Playfair MeMurrich 207 
profundus tendons and the superficial layer of the flexor brevis medius 
is, I believe, equivalent to the mammalian /umbricales. The deep layer 
of the medius, however, entering as it does into relation with the flexores 
breves profundi and the metacarpals, is probably represented in the 
mammalia by the palmar adductors, an homology which I hope to con- 
sider in detail in a later paper. It is interesting to compare the arrange- 
ment of the lumbricales in Echidna as described by Westling (1889)° 
with that which I have found in the superficial layer of the flexor brevis 
medius of the reptilia. é 
The reptilian equivalents of the sublimis tendons are indicated, [ 
believe, by the condition found in the monotremes and in certain mar- 
supials. In Ornithorhynchus a muscle has been described as the flexor 
digitorum sublimis (Smith, Westling), which has essentially the same 
relations as the flexor brevis superficialis of the reptila, and in Thyla- 
cinus and Phascogale (Cunningham, 1882), this muscle is represented 
by four minute tendons which arise from the strong tendon of the flexor 
communis digitorum. The communis tendon I take to be practically 
the homologue of the reptilian aponeurosis in which the volar cartilage 
is developed and the small tendons which arise from its surface are 
therefore equivalent to four of the slips of the flexor brevis superficialis 
of the reptilia, which have undergone, as so frequently happens, transfor- 
mation into connective tissue (see von Bardeleben and Bland Sutton). 
The identification of the tendon of the flexor communis with the 
reptiian palmar aponeurosis is not, however, quite exact, for there exists 
in the mammalia a palmar fascia which covers the sublimis tendons and 
receives the insertion of the palmaris longus. This muscle is a portion 
of the condylar flexor mass of the forearm and is, as has already been 
seen, closely related to the sublimis, containing, in the lower mammals, 
elements which in higher forms are included in that muscle. This being 
the case it must be supposed that the original insertion of the palmaris 
was with the rest of the flexor mass into the palmar aponeurosis, and that 
with the separation of the palmaris there has also been a separation of a 
palmar layer of the aponeurosis to form the mammalian palmar fascia. 
The relations of the superficial thenar and hypothenar muscles to the 
fascia support this view of its origin, since these muscles are persisting 
portions of the flexor brevis digitorum superficialis. The correct equiva- 
lent, accordingly, of the reptilian palmar aponeurosis in the mammalia 
is the tendon of the flexor communis plus the palmar fascia, but it 
should be pointed out that there is a strong probability, that the distal 
‘7 have not been able to consult this paper, but the figure which bears on this 
point is reproduced by Leche in the Mammalia-of Bronn’s Thierreich. 
