Fifteen head specimens of the yak (Bos grunniens) were dissected to study the anatomical characteristics of the nerves supplied to
a yak's eye. In the orbit, the optic nerve was “S” shaped and received 1–2 twigs from
the ciliary ganglion. The ciliary ganglion was a grayish fusiform structure, located
between the ventral branch of oculomotor nerve and retractor bulbi muscle, which gave
off 2–3 long ciliary nerves—one penetrated the sclera, and the others penetrated into
the optic nerve. In addition, there were 3–4 communicating branches from the nasociliary
nerve and the ventral branch of the oculomotor nerve. The oculomotor nerve divided
into dorsal and ventral branches; the dorsal branch divided into 4–6 twigs, two of
which supplied the rectus dorsalis muscle and the others supplied levator palpebra
superioris. The ventral branch furnished 3–5 twigs to the rectus medialis and ventralis
muscles. After it received a branch from the maxillary nerve, it finally supplied
the obliquus ventralis muscle. The trochlear nerve supplied the obliquus dorsalis
muscle. The ophthalmic nerve divided into zygomaticotemporal, frontal sinus, and nasociliary
nerves. After the zygomaticotemporal branch received a branch of maxillary nerve,
it supplied the skin of the temporal region, the lacrimal gland and the upper eyelid;
the frontal nerve supplied the lateral portion of upper eyelid; the nasociliary nerve
divided into ethmoidal and infratrochlear nerves. The ethmoidal nerve penetrated the
ethmoidal foramen, and the infratrochlear nerve supplied the upper eyelid and skin
of the frontal region. The abducent nerve supplied the rectus lateral and retractor
bulbi muscles. Therefore, the yak does not have accessory ciliary ganglion.
