The lateral distribution of muons with threshold energy \epsilon _ { \text { thr . } } \simeq 1 \times \sec { \theta } GeV have been studied in showers with energy E _ { 0 } \geq 10 ^ { 17 } eV .
The data considered in the analysis have been collected from November 2011 to June 2013 .
Experimental values are compared to predictions obtained with the use of CORSIKA code within the framework of various hadron interaction models .
The best agreement between experiment and theory is observed for QGSJETII-04 model .
At E _ { 0 } \simeq 10 ^ { 17 } eV it complies to a mixed cosmic ray composition with the mean atomic number \left < \ln { A } \right > \simeq 3.0 \pm 0.5 .
At E _ { 0 } \geq 4 \times 10 ^ { 17 } eV the composition varies around the value \left < \ln { A } \right > \simeq 0.5 .