NERVES OE EEPTILES. 313 



and the sympatlictie, together witli its ultimate distril^ution, are 

 ill the main like those in Ophidia; it exclusively supplies the 

 heart. In the Ainpliubmia the accessorius is ]5art)ally blended 

 with the vagus, and separates from it to be distributed to the 

 cervical muscles, joining branches of the first two spinal nerves. 

 In Chdonid, and CrocodlUa the accessorius blends with the gan- 

 glion of the vagus : its continuation may be recognised in the 

 posterior branch sent by the vagus to the nuchal muscles. 



The 'ninth' or hypoglossal nerve, fig. 188, 12, arises from the 

 motory tract, behind the vagus, from the trunk of which it receives 

 a branch ; it receives a smaller branch from the facial nerve ; com- 

 municates with the anterior cervical nerves ; and is distributed to 

 the muscles of the ]iliarynx and tongue, to the forked end of which 

 the lingual liranch may be traced. It sends a communicating 

 branch to those of the mandibular nerve, which are distributed to 

 the muscular floor of the mouth. In the Tortoise tlie liyp(_)glossal 

 escapes )jy two precondjdoid foramina ; after the union of these 

 origins the trunk communicates, as in Ophidia, with the vagal 

 and glosso-pharyngeal nerves : it sends a branch to the hyoid 

 muscles, a branch forward to the tongue, and a third downward 

 to the omohyoideus : the latter accompanies the vagus as far as 

 the fifth cervical. 



The vagus enters in a larger jiroportion into the formation of 

 the nerve, or rather plexus, distributing brandies to the parts to 

 which tlie source of nervous supply is ascrilicd to the hypo- 

 glossal ; but this nerve has a distinct origin by two roots in the 

 Turtle. 



The first and second spinal nerves arise, in Chelone, like the 

 hypoglossal, by motory roots only ; the sensory or dorsal roots in 

 the other cervicals are smaller than the motory ones. The skin 

 of the neck is not very sensitive : the muscles are large and 

 numerous. In the back, where muscles are few and small, the 

 sensory roots of the spinal nerves exceed the motory ones in size. 



The nerve which emerges between the first and second trunk- 

 vertebra; in Batrachia supplies the muscles and integuments of 

 the subjacent part of the throat, and sends a few filaments to 

 those of the scapula. Four of the succeeding spinal nerves 

 combine in the Salamander to form the brachial plexus : two only 

 form tliat plexus in the Frog, that emerging between the second 

 and third vertebra; being the largest. In the Crocodile the sixth 

 and seventh cervical nerves, with the two following, combine to 

 form the brachial plexus. In the Turtle the sixth, seventh, 

 eio'hth, and ninth spinal nerves constitute the brachial plexus. 



