74 
Differences in the caudifemoralis longus muscle 
The caudifemoralis longus is the main muscle retracting the femur in 
lizards and runs from the femoral trochanter posteriorly on to the 
proximal caudal vertebrae to which it attaches by multiple heads 
(see e.g. Russell & Bauer, 1992; Arnold, 1994a). The muscle is 
roughly triangular in shape and its tapering posterior section extends 
backwards to caudal vertebra 6—13 in lacertids, usually reaching 
beyond the first autotomy plane discernable in radiographs. The 
number of autotomic vertebrae to which the caudifemoralis attaches 
ranges from one to six (L. Hartley, E. N. Arnold, pers. obs). The fact 
that the muscle extends beyond the first autotomy plane means that 
some of the most posterior part of the muscle may be lost as a result 
of caudal autotomy if breakage occurs far proximally, a not uncom- 
mon event in some species, for instance Lacerta vivipara (Barbadillo 
et al., 1995). However the effect of such loss on limb function may 
be relatively small, for the bulk of the muscle lies anterior to the first 
autotomy plane and the fact that there are attachments to a number 
of nonautotomic vertebrae means that loss of the posterior section 
will not result in general loss of function. 
There is a phylogenetic regularity in the position of the first caudal 
autotomy plane discernible in radiographs. In more basal lacertids 
this is usually on the fourth to seventh caudal vertebra but in most 
Nucras and in its advanced sister group there is a posterior shift and 
the first plane is usually no further forwards than the eighth vertebra. 
This shift may mean that the bulk of the caudifemoralis longus is 
~<«— head 4 ———<$$$$=—— 





forward 
rotation 
FEMUR 
mesial lateral 
protraction a retraction 
abduction adduction 
—_—— SP 
CRUS 
METATARSAL 
SEGMENT 
DIGITS 
Fig.5 Skeleton of left hind limb of lacertid from above, showing main 
elements and regions, orientation and directions of movement. 
E.N. ARNOLD 
increased in these lizards and the proportion that remains after 
proximal autotomy is certainly larger. The number of non-autotomic 
vertebrae tends to be higher in males than females which means the 
former may possess a greater bulk of muscle to retract their rela- 
tively longer hind legs. 
General anatomy of the hind leg (Fig. 5) 
In advanced ground dwellers of the Armatured clade, the more distal 
elements of the hind limb are elongated and it is possible for the leg 
to be extended until it is more or less straight. The knee is essentially 
a ginglymus, that is a hinge joint moving mainly in a single plane, 
but does not run perpendicular to the long axis of the femur instead 
being angled mesially (Rewcastle, 1980). This results in a complex 
flexure of the crus on the femur in three dimensions. The mesotarsal 
joint between the crus and the metatarsal segment of the limb which 
runs between the astragalo-calcaneum and the other tibial bones, is 
also primarily a hinge joint and the foot can be extended in line with 
the crus or flexed until it is more or less parallel with it. However, 
these hinge joints in the hind leg do not have movement entirely 
confined to one direction. The crus can twist or swing to a small 
extent relative to the femur and the foot can flex inwards relative to 
the crus, some additional motion taking place at the base of the 
metatarsals, The foot can also twist on the crus to some extent. The 
hind limb of climbing lizards like Lacerta oxycephala is similar, but 
the distal segments are less elongated and the foot is usually in- 
flected mesially. 
Structure of the pes 
In this and following descriptions feet are assumed to be placed sole- 
down on a horizontal surface. The lacertid pes exhibits essentially 
the primitive lizard structure with no loss or increase of elements in 
the tarsus, metatarsus or phalanges, the phalangeal formula being 
2,3,4,5,4. Digits articulate with the metatarsals via ball and cup 
joints that allow considerable movement in all directions; in contrast 
the joints between the distal claw-bearing phalanges and the penul- 
timate ones are double-headed ginglymi that are tightly bound and 
only permit the claw to move in the vertical plane. 
Table 2 Characteristics of the pes in ground dwelling and climbing 
lacertids (see Figs 7-10). 
Ground dwelling 
(e.g. Acanthodactylus) 
Climbing 
(e.g. L. oxycephala) 

Relative length of 
metatarsal bones 
4 longer than 3 3 longer than 4 
Digits 14 long shorter 
Relative length of meta- 4 markedly 4 not much 
tarsal + digits 3 and 4 longer than 3 longer than 3 
Size of digit 5 short, often long 
minaturised 
Shape of digits 3-5 
in lateral view 
gently curved ventrally clearly kinked 
or straight 
Cross section rounded latero-mesially 
of digits compressed 
Shape of phalanges robust more slender 
Prepenultimate phalanx of no yes 
digits 24 markedly shorter 
than contiguous ones 
Claw long and shallow short and deep 
Articulations double-headed simple 
within digits 
Mesial flexibility restricted substantial 
of digits 14 

