The three middle metatarsals become fused together into a cannon bone; the upper part of the third middle metatarsal projects behind and forms the so-called hypotarsus, which in various ways, characteristic of the different groups of birds (with one or more sulci, grooved or perforated), acts as guiding pulley to the tendons of the flexor muscles of the toes.
Ardeae.-Piscivorous, nidicolous, waders; with complicated hypotarsus and with long cervical apteria.
Ciconiae.-Zoophagous, nidicolous, waders; with simple hypotarsus and without cervical apteria.
Nidifugous, waders; with simple hypotarsus and without cervical apteria.
How would you define hypotarsus? Add your definition here.