Orbital opening
Aditus orbitae
Definition
The orbital opening (Aditus orbitae) is nearly circular. It is limited by a prominent edge whose dorsal part or supraorbital margin (Margo supraorbitalis) is formed by the frontal and lacrymal bones, while the ventral part, or infraorbital margin (Margo infraorbitalis) belongs to the zygomatic bone.
The caudolateral part is incomplete in Carnivorous, Glires, Porcines; in these animals, the zygomatic process of the frontal bone and the frontal process of the zygomatic bone are do not reach each other at the entry of the orbit, which is opened on the temporal fossa on the dry skeleton and connected by a fibrous ligament on the living animal: the orbital ligament (Ligamentum orbitale).
In Ruminants and in Men, the two processes connect to each other and the entrance is therefore complete; it is so in Equidae, except that the zygomatic process of the frontal bone connects to the zygomatic process of the temporal bone and not to the zygomatic bone, that has no frontal process in this case.
Rostrally, the orbital margin holds the caudal lacrymal process (Processus lacrimalis caudalis) behind which is located the fossa of the lacrymal sac and the lacrymal foramen or foramina.
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