232 



THE FROG— THE PLATANA 



ganglion lies over the hypoglossal nerve. The coccygeal nerve is joined to the 

 last sympathetic ganglion by more than one branch. The sympathetic system 

 gives rise to the solar plexus on the dorsal surface of the stomach ; and the 

 nerves forming that plexus are derived mainly from the third, fourth, and fifth 

 ganglia. Anteriorly each sympathetic cord is connected with the Gasserian 

 ganglion. 



[In the Plalana this system is similar and follows the same course. There are 

 six ganglionic swellings on each cord ; and there are connections {rami communi- 

 cantes) between the ganglia and all the spinal nerves. Anteriorly each cord is 

 joined to the vagus nerve, and ends posteriorly as a broad swelling on the ninth 

 spinal nerve.] 



Make a complete sketch showing the spinal nerves and the sympathetic 

 nervous system. (See Fig. 83, A or B, page''230.) 



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 



and supplying the olfactory capsule. 

 {b) The optic nerve, which arises from the ventral surface of the brain below 



the optic lobes and supplies the retina of the eye. 

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



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. 



(iii) 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. A 

 large swelling on the trigeminal nerve is the Gasserian ganglion. 



plfactory nerve 



Cerebral lobes 



Thalamencephaloa 



Optic lobes 



Cerebellum 



Medulla oblongata- 



XJphthalmic branch 

 of Trigeminal 



Maxillary branch 



-Optic neifve 

 -Maniiibular branch 



Glossopharyngeal 



■Vagus 

 ^'Hypoglossal 



Fig. 84. — The Brain and the'principal Cranial Nerves of the Frog (Rana). 



