(e) 
(f) 
(g) 
(h) 
(i) 
(i) 
(k) 
(1) 
(m 
) 
THE CENTRAL NERVOUS SYSTEM. 277 
On the ventral surface (Fig. 85), the pons forms a broad 
commissural band extending transversely across the brain 
and upward into the supports of the cerebellum, Its surface 
is divided into two parts by a median depression, the sulcus 
basilaris, occupied by the basilar artery. 
The anterior median fissure of the spinal cord ends at the 
posterior margin of the pons in a faint depression, the fora- 
men caecum. 
The anterior funiculus of the cord is largely replaced for- 
wards by the pyramid (pyramis), a narrow band extending 
forward on either side of the middle line to the posterior 
margin of the pons. 
The trapezoid body (corpus trapezoideum) lies in the 
angle formed by the lateral margin of the pyramid with the 
posterior border of the pons. 
The fifth cranial, or trigeminal nerve (n. trigeminus), 
arises by two roots, a larger sensory root, the portio major, 
and a smaller motor root, the portio minor. The two 
parts appear at the lateral border of the pons. 
The portio major is the common trunk of the ophthalmic, maxillary 
and mandibular nerves, the portio minor joining the mandibular, so 
that the latter becomes a mixed nerve. The cut end of the portio major 
may be identified on the cranial wall and traced forward into the semi- 
lunar ganglion, the latter lying in a depression at the anterior ventral 
end of the petrosal bone. 
The sixth cranial, or abducent nerve (n. abducens), is a 
slender cord arising at the anterior end of the pyramid. 
The seventh cranial, or facial nerve (n. facialis), and the 
eighth, or acoustic nerve (n. acusticus), arise from the 
lateral margin of the trapezoid body. 
The two nerves are closely associated, the former being slightly 
anterior in position. Its chief portion is the motor root. In addition 
the nerve receives a sensory filament, the portio intermedia or inter- 
mediate nerve. 
The glossopharyngeus, vagus, and accessorius arise by 
several roots arranged in a linear series along the lateral 
margin of the medulla. The trunk of the accessorius ex- 
tends backward on the spinal cord, its roots, about ten in 
number, arising as far back as the fifth cervical spinal nerve. 
The twelfth cranial, or hypoglossal nerve (n. hypoglossus), 
arises by several roots from the ventral surface of the medulla 
