The twin on the left is in anterior longitudinal presentation and its right leg is retained. The twin on the right is in posterior longitudinal presentation with both legs extended. To differentiate a front leg from a hind leg count the number of joints below the hock or the elbow, which feel similar inside the cow. There are two joints below the elbow and there is only one joint below the hock. It is usually advisable to deliver the twin in posterior presentation first.
Drost M (1976)