THE NERVOUS SYSTEM 107 



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 in- 

 ferior obliques. These muscles move the eye. 



The fourth nerves (trochlear) emerge from the dorsal 

 side of the brain behind the posterior coUiculus, run for- 

 ward 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 throug'h 

 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 fora- 

 men 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 fora- 

 men, 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. Imme- 

 diately 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 re- 

 gion of the medulla oblongata, course along under the 

 brain beside the third cranial nerves, emerge into the orbits 



