The function is to protect the area between the nail and epidermis from exposure to harmful bacteria.
Beneath the cuticle is a thin layer of pterygium.
The vascularization pattern is similar to that of perionychium.
The Eponychium in Hooved Animals
"The term Eponychium is used to describe the deciduous hoof capsule in veterinary-medical and embryological literature. In other aspects of veterinary medicine, the term is generally reserved for the perioplic corium of the permanent hoof. Epidermal tubules and lamellae are already present in the non-cornified fetal hoof epidermis. These structures, along with the formation of a white line, allow this epidermis to be divided into the same segments as are commonly used when referring to the permanent hoof. The greatest part of the deciduous hoof epidermis consists of the sole and frog, with significant portions forming in the coronary corium and that of the hoof wall as well. The perioplic corium only makes up insignificant portions of the fetal hoof capsule, however. Between the second half of the gestation period and birth, this deciduous (primary) hoof capsule is continually being replaced from below by newly-forming, cornified permanent hoof capsule." On the basis of its structure and origin, it is suggested that the term "deciduous hoof capsule (Capsula ungulae decidua)" be used as a replacement for the word "Eponychium" when referring to the primary hoof epidermis.
Bragulla H. [The deciduous hoof capsule (Capsula ungulae decidua) of the equine fetus and newborn foal]. Anat Histol Embryol. 1991 Mar;20(1):66-74.