504 Animal Biology 



rigemina, act as centers for auditory and visual reflexes. Important path- 

 ways to and from other parts of the brain pass through the midbrain. 



The pons (Figs. 246 and 247) Hes in front of the cerebellum and above 

 the medulla. Its fibers connect the two halves of the cerebellum and join 

 the medulla with the midbrain. 



The medulla oblongata (Figs. 246 and 247) lies between the pons and 

 the spinal cord, being much like the latter structurally. The fourth 

 ventricle of the brain is located within the medulla and connects with 

 the central canal of the cord. The medulla contains such vital centers 

 as cardiac, respiratory, and vasoconstrictor centers, the latter for the con- 

 trol of arterial pressure. 



The twelve pairs of cranial nerves (Fig. 247) may be summarized as 

 follows : 



1. Olfactory — sense of smell 



2. Optic — sense of sight 



3. Oculomotor — control of following eye muscles: ciliary, inferior 

 oblique, superior, inferior, and internal (medial) recti, sphincter of the 

 iris of eye 



4. Trochlear (pathetic) — superior oblique muscle of eye 



5. Trigeminal — sensory to the head, motor for the muscles of mastica- 

 tion 



6. Abducent — external (lateral) rectus of the eye 



7. Facial — motor to the face and scalp; sensory to the tongue, secre- 

 tory to the submaxillary and sublingual (salivary) glands of the mouth 



8. Acoustic (auditory) — to cochlear part of the ear for hearing, to 

 vestibular part of the ear for equilibrium 



9. Glossopharyngeal — -motor to pharynx; sensory to tongue, mucous 

 membranes of pharynx, tonsils, Eustachian tube, tympanic cavity of the 

 ear; secretory to the parotid gland (salivary) of mouth. 



10. Vagus (pneumogastric) — sensory to larynx, trachea, lungs, esopha- 

 gus, stomach, small intestine, part of large intestine; motor for respira- 

 tion, heart action, digestion (inhibits heart action) ; secretory for gastric 

 and pancreatic glands, 



11. Accessory — the cranial part to the pharyngeal and superior laryn- 

 geal branches of vagus; the spinal part to the trapezius (of back) and 

 sternocleidomastoid (neck) muscles 



12. Hypoglossal — motor to tongue 



The sensory nerves of the skin transmit sensations of pressure, pain, 

 heat, and cold from the specific sense organs to the proper parts of the 



