Table 2.

Descriptive statistics of the friction measurements

Orientation	Roughness Ra (in μm)	N	Dorsal scales (mean ± SD)	Lateral scales (mean ± SD)	Ventral scales (mean ± SD)
Rostrad	0.08	52	0.454 ± 0.069	0.412 ± 0.093	0.207 ± 0.038
Rostrad	0.25	52	0.367 ± 0.058	0.353 ± 0.074	0.218 ± 0.042
Rostrad	0.42	52	0.325 ± 0.052	0.311 ± 0.053	0.203 ± 0.066
Rostrad	1.11	52	0.300 ± 0.043	0.268 ± 0.064	0.170 ± 0.037
Rostrad	2.26	52	0.293 ± 0.044	0.280 ± 0.075	0.153 ± 0.032
Rostrad	2.75	52	0.272 ± 0.040	0.281 ± 0.062	0.161 ± 0.022
Rostrad	12.67	52	0.261 ± 0.050	0.250 ± 0.035	0.144 ± 0.019
Rostrad	13.94	52	0.283 ± 0.056	0.301 ± 0.063	0.151 ± 0.027
Rostrad	*	52	0.299 ± 0.067	0.346 ± 0.079	0.163 ± 0.038
Caudad	0.08	52	0.472 ± 0.067	0.416 ± 0.090	0.227 ± 0.055
Caudad	0.25	52	0.384 ± 0.076	0.349 ± 0.075	0.222 ± 0.043
Caudad	0.42	52	0.344 ± 0.058	0.320 ± 0.066	0.204 ± 0.057
Caudad	1.11	52	0.308 ± 0.048	0.283 ± 0.072	0.165 ± 0.032
Caudad	2.26	52	0.301 ± 0.048	0.289 ± 0.081	0.153 ± 0.025
Caudad	2.75	52	0.271 ± 0.040	0.283 ± 0.060	0.162 ± 0.029
Caudad	12.67	52	0.266 ± 0.037	0.279 ± 0.049	0.157 ± 0.043
Caudad	13.94	52	0.303 ± 0.059	0.307 ± 0.043	0.181 ± 0.063
Caudad	*	52	0.375 ± 0.090	0.408 ± 0.092	0.188 ± 0.055
Sideward	0.08	94	0.455 ± 0.061	0.408 ± 0.086	0.233 ± 0.037
Sideward	0.25	94	0.402 ± 0.061	0.348 ± 0.075	0.242 ± 0.036
Sideward	0.42	94	0.333 ± 0.049	0.310 ± 0.046	0.220 ± 0.040
Sideward	1.11	94	0.310 ± 0.038	0.273 ± 0.051	0.191 ± 0.025
Sideward	2.26	94	0.297 ± 0.046	0.283 ± 0.065	0.185 ± 0.020
Sideward	2.75	94	0.287 ± 0.040	0.284 ± 0.046	0.194 ± 0.021
Sideward	12.67	94	0.297 ± 0.042	0.289 ± 0.039	0.212 ± 0.028
Sideward	13.94	94	0.322 ± 0.057	0.362 ± 0.061	0.221 ± 0.031
Sideward	*	94	0.360 ± 0.068	0.437 ± 0.106	0.234 ± 0.045

Shown are the mean friction coefficients for all roughnesses for dorsal, lateral and ventral scales. An asterisk in the roughness column stands for the roughness of the P60 sandpaper which was not measurable