484 The Phylogeny of the Palmar Musculature 
from the ulnar side of the profundus tendon to the index and is inserted 
into the ulnar side of the sheath of that tendon. The first lumbrical 
in Liolepisma has also two insertions, but in Iguana it passes only to 
the ulnar side of its digit; in the opossum it has only one portion | 
which passes to the radial side of the index. It may be stated that 
von Bardeleben (1902) mentions incidentally the occurrence of two 
portions in the lumbricals of certain mammals.” 
I was not able to detect any indications of a doubling of any of the 
lumbricals in either the cat (Fig. 8) or the mouse (Fig. 9), in both of 
which the muscles present the usual mammalian relations. The fact 
that we have a bilateral insertion for the second and third lumbricals 
in the lacertilia inclines one to the view that the doubled condition 
of the corresponding mammalian muscles may be a relic of the rep- 
tilian arrangement. There is, however, another possibility, namely, 
that the smaller slips of the mammalian muscles represent persistent 
portions of a stratum profundum of the flexor brevis superficialis. 
In Callisaurus slips from this stratum pass to the second, third and 
fourth digits, and these slips are associated at their insertions with 
the sheaths of the corresponding profundus tendons. It is not at all 
impossible that the smaller slips of the second and third lumbricals of 
the opossum may represent the corresponding portions of the stratum 
profundum of the reptilian flexor brevis superficialis, the portion to the 
third digit being indistinguishable. 
Which of these two views may be the correct one the material I have 
had for study does not determine. The nerve supply of the various 
slips, so far as my observations go, throws no light on the question. 
We come now to the consideration of the stratum profundum * of the 
flexor brevis medius, being the first of the three layers described by 
Cunningham and that which is constituted by the adductor muscles 
of the mammalian hand. The arrangement of these muscles in the 
opossum has been well described by Young (1879) and Brooks (1886), 
but on comparing their descriptions a slight difference in the limita- 
tions of one of the muscles is noticeable, a portion of the muscle recog- 
nized by Brooks as the adductor pollicis, namely, its ulnar head, being 
regarded by Young as a portion of his flexor brevis pollicis, 7. ¢., of 
the intermediate layer of the pollical muscles. My observations lead 
me to agree with Young on this point, the relatively thick muscle 
2Von Bardeleben refers to certain observations of his own upon this point which 
I have not been able to consult. 
3IT use this term here in a strictly mammalian sense. The stratum is probably 
equivalent to the str. medium of the reptilian hand. 
