Yonago Acta medica 2012;55:75–80

A Case of the Bilateral Duplicate Palmaris Longus Muscles
Coupled with the Palmaris Profundus Muscle
Yuichi Takanashi, Masaki Eda, Toshiyuki Kaidoh* and Takao Inoué
Division of Morphological Analysis, Department of Anatomy, School of Medicine, Tottori University
Faculty of Medicine, Yonago 683-8503, Japan and *Division of Medical Morphology, Department of
Anatomy, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8503, Japan
The palmaris longus muscle is one of the most variable muscles in human anatomy. During aroutine anatomical dissection for medical students at Tottori University, we found duplicate
palmaris longus muscles in the bilateral forearms together with the palmaris profundus muscle in the right forearm. The bilateral aberrant palmaris longus muscles were observed at theulnar side of the palmaris longus muscle and their distal tendons were attached to the flexor
retinaculum. The palmaris profundus muscle found in the right forearm was located at theradial side of the flexor digitorum superficialis muscle. The proximal tendon was originatedfrom the anterior surface in the middle of the radius, while the distal tendon coursed radial
to the median nerve through the carpal tunnel, finally inserting into the distal part of theflexor retinaculum. Both the palmaris longus and aberrant palmaris longus muscles were innervated by the median nerve. The palmaris profundus muscle was presumably supplied by
the median nerve.
Key words: cadaver; forearm; regional anatomy; skeletal muscle
coupled with the PP. In this paper, we describe myological findings and innervation of this rare case.

The palmaris longus muscle (PL) is located in the
superficial layer of the anterior surface of the forearm. It has a small belly arising from the medial
epicondyle of the humerus, and its long thin tendon
inserts into the palmar aponeurosis in the hand. The
muscle is one of the most variable muscles in thehuman body (Takafuji et al., 1985). During an anatomical dissection for medical students at Tottori
University in 2011, we found a pair of the duplicate
PL in the bilateral forearms. Furthermore, the palmaris profundus muscle (PP), which is not usuallyexist, was found in the right forearm. Although the
duplicate PL is frequently reported (Reimann et al.,
1944; Hojo, 1976; Kimura et al., 1979; Xue et al.,
1998; Zeybek et al., 1998; Kawashima et al., 2002),
it is rarely seen in bilateral forearms. In addition,
there are no reports on the bilateral duplicate PL

Materials and Methods
Anomaly of the PL was noticed on both sides of a57-year-old Japanese male cadaver. We observed
closely the origin and insertion of the muscles,
finely dissected the region of interest, and examinedmuscle shape and nerve supplies macroscopically,and photographed. We also measured the size of themuscles and tendons using a vernier caliper. The
length of a muscle belly was measured between
the origin (medial epicondyle) and the most distal
part of the muscle-tendon border. The length of PL
tendon was measured from the most distal part ofAbbreviations: FCR, flexor carpi radialis muscle; FCU, flexor carpi ulnaris muscle; FDS, flexor digitorum superficialis muscle; PL, palmaris longus muscle; PP, palmaris profundus muscle; PT, pronator teres muscle

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the muscle-tendon border to the baseof palmar aponeurosis, whereas that ofaberrant PL was done from the identical point to the attachment to the flexor
retinaculum. The width of muscle belly
was measured at the maximum width.
The width and thickness of the bothPL and aberrant PL were measured at
the midpoint of the entire length of thetendon.
Results
The duplicate PL and their nerve supply found in the bilateral forearms areshown in Figs. 1 and 2, respectively.
Their measurements, myological findings and nerve innervations are summarized in Table 1. The PP in the rightforearm is shown in Fig. 3. No othermuscular anomaly was recognized in
the body.
Duplicate PL in the right forearm
The aberrant PL was found ulnar to
the PL (Fig. 1a). The bellies and tendons of both the aberrant PL and PL
were closely apposed with each other.
The duplicate PL arose from a common tendinous origin of flexor muscles[PL, flexor carpi radialis muscle (FCR),
flexor carpi ulnaris muscle (FCU), pronator teres muscle (PT) and a part of
the flexor digitorum superficialis mus- Fig. 1. Photographs of superficial flexor muscles of the forearm. Notecle (FDS)] at the medial epicondyle of PLa between PL and FCU. a: right side, b: left side. FCR, flexor carpi
radialis muscle; FCU, flexor carpi ulnar muscle; PA, palmar aponeurosis;
the humerus.
PL, palmaris longus muscle; PLa, aberrant palmaris longus muscle.
In the PL, the muscle belly measuring 110 mm in length and 12.6 mm
followed by the tendon distally at the middle ofin width, was followed by a long tendon distally at
forearm, and finally inserting into the flexor retithe middle of the forearm. The tendon coursed overnaculum (Table 1).
the flexor retinaculum, finally inserting into the palBoth the PL and aberrant PL were innervatedmar aponeurosis (Table 1).
by branches of the median nerve in the proximal
The morphology of the aberrant PL was quite
third of the forearm (Fig. 2a). The branches to thesimilar to that of the PL. The muscle belly meaFCR, PL and FDS arose as a common trunk fromsuring 135 mm in length and 10 mm in width was76Aberrant palmaris longus muscles

Fig. 2. Photographs showing the median nerve and its branches to flexor muscles. The belly of the pronator teres is cut
and opened for the demonstration of the innervation. Arrowheads show the common trunk of the median nerve to the PL
and PLa. a: right side, b: left side. FCR, flexor carpi radialis muscle; FDS, flexor digitorum superficialis muscle; M, median nerve; PL, palmaris longus muscle; PLa, aberrant palmaris longus muscle; PT, pronator teres muscle.

by a long tendon distally at the middle of the forearm. The tendon coursed over the flexor retinaculum, finally inserting into the palmar aponeurosis(Table 1).
The morphology of the aberrant PL was quite
similar to that of the PL. The muscle belly measuring 145 mm in length and 8.3 mm in width was
followed by the tendon distally at the middle offorearm, and finally inserting into the flexor retinaculum (Table 1).
Similarly to the right forearm, both the PL andaberrant PL were innervated by branches of the median nerve in the proximal third of the forearm (Fig.
2b). However, the ramification of the branch wasdifferent. The branches to the FCR, PL, aberrant PL
and FDS arose as a proximal common trunk fromthe median nerve, and another single branch to FDS
arose distally from the median nerve.

the median nerve, whereas those to the aberrant PL
and FDS arose as another common trunk whichbranched distally.
Duplicate PL in the left forearm
The morphological findings of the duplicate PL in
the left forearm are fundamentally identical to thosein the right forearm.
The aberrant PL was also found ulnar to the
PL (Fig. 1b). The bellies and tendons of both theaberrant PL and PL were closely apposed with eachother. The duplicate PL arose from a common tendinous origin of flexor muscles (PL, FCR, FCU, PT
and a part of the FDS) at the medial epicondyle ofthe humerus.
In the PL, the muscle belly measuring 130
mm in length and 10 mm in width was followed77

Y. Takanashi et al.

Table 1. Summary of PL and aberrant PL
PL

Aberrant PL

Right
Muscle belly
TendonLengthWidth
LengthWidthThickness

(mm)
(mm)
(mm)
(mm)
(mm)

OriginInsertion
Innervation

Left

Right

110.0
130.0
135.0
12.6
10.0
10.0
155.0
140.0
105.0
3.8
3.8
6.2
1.1
1.1
0.6
Medial epicondyle Medial epicondyle Medial epicondyle
Palmar aponeurosis Palmar aponeurosis Flexor retinaculumMedian nerve
Median nerve
Median nerve

Left
145.0
8.3
100.0
6.2
0.7
Medial epicondyle
Flexor retinaculumMedian nerve

PL, palmaris longus muscle.

(Koganei et al., 1903), 2.1% (Adachi, 1910), 2.5%
(Sato et al., 1974), whereas 3.1% in Russians (Gruber,1868) and 0.8% in Americans (Reimann et al.,1944).
Most of the duplicate PL thus far reported
were unilateral. As far as we know, there was only
one report of the duplicate PL in both forearms(Kimura et al., 1979). As for the occurrence of theaberrant PL in the duplicated PL, it is mostly located at the ulnar side of PL as observed in the present
study (Xue et al., 1998), but occasionally at the radial side (Kawashima et al., 2002). The aberrant PL
is innervated by the median nerve as was observedin the present study (Kimura et al., 1979; Takafuji etal., 1985; Xue et al., 1998; Kawashima et al., 2002),
but occasionally doubly innervated both by the median and ulnar nerve (Xue et al., 1998).
The PP is another case of the anomaly of the
PL. It originates from the anterior surface of theradius terminating to the flexor retinaculum of the
deeper layer of the palmar aponeurosis (Reimann etal., 1944). Yoshida et al. (1983) observed variationsof the deep flexor group of the antebrachial muscles
and classified them into four types. Our case corresponds to the type 2 (palmaris profundus longus
muscle) of their classification. The present case isalso analogous to that reported by Stark et al. (2010).
Humphry (1872) proposed the idea that the superficial layers of the forearm flexor muscles are derived
from radial, intermediate, and ulnar sectors in theventral matrix of the elbow (Howell, 1936a). According to this hypothesis, the PT and FCR are
differentiated from the radial sector, the FCU fromPP in the right forearm
The PP in the right forearm was located at the radial side of the middle part of FDS. It was spindle
in shape with slender tendons on both ends. The
proximal tendon was apparently independent to
the radial head of the FDS and originated from theanterior surface in the middle of the radius. The
muscle belly measured 77 mm in length. The distal
tendon measuring 45 mm in length coursed radial
to the median nerve under the flexor retinaculum.
It passed through the carpal tunnel together withthe median nerve, and finally inserted into the distal part of flexor retinaculum (Fig. 3). Since the PP
coursed in the vicinity of the median nerve, themuscle was presumably supplied by the median
nerve. The branch to the muscle could not be macroscopically demonstrated.

Discussion
The variation of the PL was classified by Reimann
et al. (1944) as follows: complete agenesis, variationin the location and form of the fleshy portion, aberrancy in the attachment at either extremity, duplication or triplication, accessory slips or substitutionsof similar form or position. In particular, duplicate
PL has been frequently reported (Reimann et al.,
1944; Hojo, 1976; Kimura et al., 1979; Xue et al.,
1998; Zeybek et al., 1998; Kawashima et al., 2002).
The occurrence of duplicate PL in Japanese is 1.9%78

Aberrant palmaris longus muscles

As for the PP, Takisawa et al. (1979) considered that
the PP is derived from the radial sector.
From a viewpoint of phylogeny, the PL isabsent in the lowest class of mammals such as
Monotremata (Platypus) (Howell, 1936b). With theprogress of the locomotion in hands, the palmar
aponeurosis has appeared. Although the PL inserts
to the aponeurosis in the human, the final insertionis different in animals: the proximal phalanx in theunau (Humphry, 1869), kinkajou and genet (Parsons,1898); the flexor retinaculum in the tamandua(Windle and Parsons, 1899); both the palmar aponeurosis and flexor retinaculum in the chimpanzeeand cynocephalus (Champneys, 1871). Since theaberrant PL and PP insert into the flexor retinaculum, these muscles are considered to be a kind of
atavism.
The PL and PP are of clinical importancefrom viewpoints of tendon grafts and carpal tunnel
syndrome, respectively. The PL is frequently used
as a donor tendon for ligament reconstruction including elbow, wrist and so on (Nestor et al., 1992;
Ogunro, 2007; Whitaker et al., 2008). Although
the duplicate PL is not so frequently occurred as
mentioned above, it will provide a useful grafts in
tendon surgery when found in patients. Since thedistal tendon of the PP courses in the vicinity of themedian nerve as seen in this study, it sometimes
compresses the median nerve, causing a carpal tunnel syndrome (Floyd et al., 1990; Server et al., 1995;
Miyoshi et al., 2000). It is interesting that the PP
reflecting the old phylogenetic pattern occasionallycause a carpal tunnel syndrome. It is also importantto pay a special attention of the presence or absenceof the PP in this syndrome.

Fig. 3. Photograph of the anterior side of the right forearm, showing the palmaris profundus muscle (PP witharrow). The flexor retinaculum is transected and turned
over. The tendon of the flexor carpi radialis is cut for thedemonstration of the distal tendon of the palmaris profundus muscle. FCR, flexor carpi radialis muscle; FCRt, tendon of flexor carpi radialis muscle; FDS, flexor digitorum
superficialis muscle; FR, flexor retinaculum; PP, palmaris
profundus muscle.

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Received September 27, 2012; accepted October 26, 2012
Corresponding author: Yuichi Takanashi

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