76 
a 
E.N. ARNOLD 
b 
Fig. 8 Dorsal views of right pes of lacertids (digit 1 to left). a. Ground dwelling Acanthodactylus erythrurus: metatarsal 4 longest, digit articulations 
double headed, digit 5 miniaturised. b. Rock climbing Lacerta oxycephala: metatarsal 3 longest, digit articulations single, digit 5 large, phalanges 
slender, intermediate ones in digits 3 and 4 relatively short. For other differences, see Table 2. 
bones 1—4, and the digits that arise from them, are quite short. The 
metatarsals and digits exhibit an increase in length from number | to 
3 but metatarsal 4 is shorter than metatarsal 3 and, although digits 1— 
4 increase in length, the shortness of metatarsal 4 results in digit 4 
projecting only a comparatively short distance beyond digit 3. Digit 
5 is relatively long and unminiaturised, the articulation of its second 
and third phalanges being about level with the distal end of metatar- 
sal 4. When at rest, digits 3-5 are distinctly kinked in the sagittal 
plane with abrupt changes of direction along their length (Fig. 9b— 
d). In digit 3, phalanx 2 is directed downwards, 3 upwards and 4 
downwards. In digit 4, phalanx 2 is directed downwards, 3 ap- 
proaches the horizontal, 4 is flexed upwards and-5 downwards. In 
digit 5, phalanx 2 is directed upwards, 3 is roughly horizontal and 4 
flexed downwards, but there is sometimes marked deviation from 
this pattern (see p. 77). Kinking when digits are at rest appears to be 
maintained partly by the form of the envelope of skin that surrounds 
each digit and that of the ligamentous connexions that surround each 
interphalangeal joint. If the digit of a live lizard is stretched by 
pulling the claw, kinking disappears temporarily, but it is transiently 
increased if the tension in the tendons lying dorsal and ventral to the 
phalanges is raised by the action of the muscles that activate them. 
Kinking is often especially marked in animals preserved in alcohol 
or formalin because shrinkage of muscle tissue produces similar 
tension in the tendons. 
The digits are mesiolaterally compressed when transversely sec- 
tioned through a phalanx (Fig. 10b), instead of having a more 
rounded profile like ground dwellers. This difference results from 
the relative thicknesses of the phalanges and the surrounding ten- 
dons, especially the ventral ones. In ground dwellers the latter may 
be considerably more slender than the robust phalanges above them, 
while in climbers like Lacerta oxycephala, where the phalanges are 
more delicate in build, the stout ventral tendons may be as thick as 
thicker than these. The penultimate phalanx of each digit is long and 
gently curved downwards while phalanx 2 in digit 3 and phalanges 
2 and 3 in digit 4 are shorter than those proximal and distal to them. 
The terminal phalanx of each digit and the claw that covers it is short, 
