J. Playfair McMurrich 479 
metacarpo-phalangeal joint, and this and its representatives in other 
mammals I shall speak of as the flexor brevis minim digit, reserving 
until later the question as to the propriety of the use of that name. 
A third portion (Fig. 6, v) is recognizable as a rather small slip 
arising from the volar surface of the sheath for the long tendons (the 
anterior annular hgament) close to the ulnar side of the tendon of the 
palmaris longus (pl), passing thence obliquely ulnarwards to fade out 
in the sheath of the tendon of the flexor profundus digitorum to the 
minimus. I found that the sublimis tendon of the fifth digit separates 
in the opossum from the palmaris longus and it seems not impossible 
that the slip now under consideration may represent an undegenerated 
portion of the flexor brevis superficialis from which that tendon has 
been differentiated. The probability of such an interpretation of the 
shp is strengthened by the fact that a small amount of muscle tissue 
persisted in the specimen I studied by sections (an embryo of 6.5 em.) 
on either side of the sublimis tendons of the third (Fig. 7, ~) and second 
digits. 'The presence of these slips seems to furnish strong confirma- 
tion of the views I have maintained as to the morphological significance 
of the sublimis tendons, the opossum in respect to the persistence of 
these slips as in so many others furnishing indications of a connecting 
link between the reptilia and the higher mammalia, in which, so far 
as my experience and information go, this median portion of the flexor 
brevis superficialis is entirely unrepresented by muscle tissue. 
In addition to the muscles so far named there is a well developed 
abductor minimis digiti, whose origin is contiguous to that of the flexor 
brevis minimi digiti though extending a little farther proximally and 
whose insertion is into the ulnar side of the base of the proximal 
phalanx. 
The muscles of the hand of the opossum have been studied with 
special reference to their arrangement in layers by Young (1879) and 
Brooks (1886%) who adopt essentially Cunningham’s plan. In the 
identification of the individual muscles of the little finger there are 
certain discrepancies between these two authors, and my results, while 
agreeing in the main with those obtained by Brooks, differ somewhat 
even from his. Thus what Young has termed the abductor minimi 
digiti is, as Brooks has pointed out, the flexor brevis, while Young’s 
opponens is the true abductor. Young failed to observe the slip which 
I have regarded as a muscular portion of the flexor sublimis, though 
Brooks figures it and speaks of it as the flexor brevis digitorum manus. 
Neither author makes mention of the palmaris brevis which might 
readily be overlooked in dissections on account of its thinness and its 
relation to the fascia. 
