3. The Cranial Nerves. 



Expose the brain and note the following cranial nerves : — 



(a) The olfactory nerve, arising from the anterior end of the olfactory 



lobes, supplying the olfactory capsule. 



(b) The optic nerve, arising from the ventral surface of the brain below 



the optic lobes, supplying the retina of the eye. 



(c) The trigeminal nerve, arising just behind the optic nerve, giving 



rise to the following branches : — 



(i) The ophthalmic nerve, which passes over the muscles of the eye 



and supplies the skin in the region of the olfactory capsule. 

 (ii) The maxillary nerve, which runs . forward under the eyeball, 



and supplies the skin covering the upper jaw. 

 (hi) The mandibular nerve, which is at first continuous with the 



maxillary, and then bends round the inner surface of the upper 



jaw to extend along the outer surface of the mandible. 



Brachial plexus 



Glossopharyngea 

 nerve - - 



Lingual artery 

 Hypoglossal nerve 



Spinal 6- 

 Dorsal aorta- 

 Spinal 1- 

 Sciatic plexus Spinal 8 

 Spinal » 



Glossopharyngeal 



nerve |- 



Vagus nerve" 



.Cerebral 

 hemispheres 



-Thalamencephalon 



Optic lohes 

 Cerebellum 



Medulla oblongata 



Hypoglossal 

 (1st spinal nerve) 



Fig. 18. — Brain. Cranial Nerves. Spinal Nerves, and Sympathetic Nervous System of 



Xenopus and Rana. 



(d) The glossopharyngeal and the vagus (or pneumogastric) nerves, 

 leaving the skull together, immediately behind the auditory capsule. 

 The glossopharyngeal passes along in front of the hypoglossal nerve 

 and proceeds along the base of the tongue. The vagus, after giving 

 off branches to the dorsal muscles, reaches the walls of the pharynx 

 and run obliquely backwards to supply the pharynx, heart, lungs 

 and stomach. 

 Make a complete sketch showing the brain and the above-mentioned 

 cranial nerves. 



46 



