360 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



greater central mass of the diencephalon and in mammals is subdivided into several parts. 

 The epithalamus consists of the pineal body and other evaginations from the roof of the 

 diencephalon, and adjacent parts. 



12. The mesencephalon or midbrain is composed dorsally of the optic lobes, of which 

 there are two in most vertebrates, four in mammals, named the corpora quadrugemina. 

 Ventrally the midbrain consists of the tegmentum and the cerebral peduncles. 



13. The metencephalon includes the cerebellum dorsally and the pons ventrally. The 

 pons is distinctly developed only in mammals. 



14. The myelencephalon becomes the medulla oblongata. 



15. The brain is hollow, its cavities being known as ventricles. The first two ventricles 

 are in the cerebral hemispheres, the third ventricle in the diencephalon, the fourth in the 

 medulla. In lower vertebrates ventricles are also present in the cerebellum and midbrain. 

 The ventricles are connected with each other. 



16. The brain of fishes and Amphibia is provided with ten cranial nerves, that of 

 amniotes with twelve. The last two in amniotes are probably not new formations. 



17. The first or olfactory nerve extends from the olfactory epithelium in the nose to 

 the olfactory bulbs. 



18. The second or optic nerve extends from the retina to the diencephalon. It is not 

 a true nerve but a tract of the brain. 



19. The third or oculomotor nerve is a motor nerve to the inferior oblique, superior, 

 inferior, and internal recti and some accessory muscles of the eyeball. It originates in the 

 midbrain. 



20. The fourth or trochlear nerve is a motor nerve to the superior oblique muscle of 

 the eyeball. It arises from the midbrain. 



21. The fifth or trigeminus nerve is the chief somatic sensory nerve of the head and the 

 nerve of the first visceral or mandibular arch. It has in all vertebrates three branches: 

 the ophthalmic (deep ophthalmic of fishes) branch to the orbit and nasal region; the maxillary 

 to the upper jaws and roof of the mouth and pharyngeal cavities; the mandibular to the lower 

 jaw and floor of these cavities. The first two are pure somatic sensory nerves; the man- 

 dibular also contains visceral motor fibers to the visceral muscles belonging to the lower jaw. 

 In fishes there is an additional branch of the trigeminus, the superficial ophthalmic, which 

 disappears later. The trigeminus arises from the anterior end of the medulla. 



22. The sixth or abducens nerve is the motor nerve of the external rectus muscle of the 

 eyeball. It takes origin in the floor of the medulla. 



23. The seventh or facial nerve is the nerve of the second or hyoid visceral arch. It is 

 large in fishes because it includes branches for the lateral line system. These disappear in 

 land vertebrates, leaving only that part of the facial which is named the hyomandibular 

 nerve in fishes. This nerve is a sensory nerve (taste) to the pharyngeal cavity and a visceral 

 motor nerve to the muscles of the hyoid arch. The facial springs from the medulla. 



24. The eighth or auditory nerve is a sensory nerve extending from the internal ear to 

 the acustic area of the medulla. 



25. The ninth or glossopharyngeal nerve is the nerve of the third visceral arch. In 

 the land vertebrates it is reduced but continues to supply sensory fibers to the floor of the 

 pharyngeal cavity and visceral motor fibers to pharyngeal muscles. It is attached to the 

 medulla. 



26. The tenth or vagus nerve is the nerve of the remaining visceral arches. In fishes 

 it also includes a large branch for the lateral line. With the loss of the lateral line system and 

 the branchial mode of breathing the vagus is much reduced but continues to supply the 

 corresponding region of the pharynx, being a sensory nerve to the lining of this region and a 



