Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/121

Rh on the under side of the brain. They enter the orbits through the anterior lacerated foramina and innervate the superior, inferior, and internal rectus muscles, and the inferior obliques. These muscles move the eye.

The fourth nerves (trochlear) emerge from the dorsal side of the brain behind the posterior coLLiculus, run forward along the under surface of the cerebral hemispheres lateral to the second and sixth nerves, and enter the orbits through the anterior lacerated foramina. They innervate the superior oblique muscles of the eye.

Each of the fifth nerves (trigeminal) leaves the pons as two closely connected roots. It then divides into three branches. (1) The ophthalmic branch passes through the anterior lacerated foramen into the orbito-temporal fossa, where it sends branches to the adjacent integument, and a small nerve back into the cranium through a foramen which is anterodorsal to the optic foramen. (2) The superior maxillary is a large branch which also enters the orbito-temporal fossa through the anterior lacerated foramen, runs along the dorsal side of the alveolar process of the maxillary bone, traverses the infraorbital fissure, and terminates at the roots of the vibrissae and in the skin of the face. (3) The inferior maxillary nerve passes from the cranial cavity through the foramen ovale. Immediately after emerging from the cranium it gives off several branches to the jaw muscles, a lingual ramus to the tongue, while a large trunk enters the mandibular foramen of the mandible. This trunk traverses the dental canal, emerging by the mental foramen to pass to the skin of the lower jaw and the chin. If time permits, trace the nerve through the mandible.

The sixth nerves (abducens) start from the anterior region of the medulla oblongata, course along under the brain beside the third cranial nerves, emerge into the orbits