While investigating the cause of entrapment syndrome of the peripheral nerves in the elbow region, we observed variability of the pronator teres muscle and the relationship of this muscle to the median nerve and the surrounding vessels. Attention was also paid to the occurrence of the supracondylar process of the humerus and Struthers' ligament with regard to their ontogenetic and phylogenetic development. For this purpose, a classical anatomical dissection of the upper limbs of 68 adults, three fetuses and a phylogenetic assessment of five mammalian species was performed. In terms of variability in the anatomical structures of the elbow region, we found the most serious clinical condition to be where the median nerve ran through the pronator canal together with the ulnar vessels (1.5%), or when it passed through the ulnar head of the pronator teres (5.9%). The pronator teres examined by us in fetuses showed the same arrangement as in adult individuals, including the created ulnar head. The occurrence of a supracondylar process and Struthers' ligament was not observed in our collection. The presence of these structures was not confirmed during the fetal period, either. The phylogenetic part of the study re-opened the question of the meaning and function of the entepicondylar foramen, because we noted differences in the occurrence of this structure in two related genera with a very similar way of life (Djungarian hamster and golden hamster).