ANATOMY. 



sends off' branches : these, again divided, 

 form ramifications : and *in their further 

 progress form twigs, filaments, Stc. and 

 this division goes on, until the nerve, from 

 its smallness, can be no longer traced. 

 Yet we can manifestly discern the nerves 

 in some instances, as in the organs of 

 sense, terminating in a pulpy expansion. 



Like the arteries, nerves communicate 

 with each other; and it is conjectured 

 that these communications, like those of 

 the blood-vessels, are designed to obviate 

 the effects of the injury of compression of 

 any particular nervous trunk. In some 

 parts these communications are very nu- 

 merous, so as to constitute a minute net- 

 work of nervous filaments, called a plexus. 



Description of the particular nerves. 

 There are in the whole body thirty-nine 

 pairs of nerves ; of which nine arise from 

 the brain, and thirty from the spinal mar- 

 row. There is another pair, called the 

 great sympathetic, which can hardly be 

 ascribed to either of these classes. 



Nerves of the brain. 



1st pair. Olfactory nerves ; arise from 

 the corpora striata, and go through the 

 cribriform lamella of the ethmoid bone to 

 the pituitary membrane of the nose. 



2d pair. Optic nerves ; arise from the 

 Ihalami nervorum opticorum, and proceed 

 to the eye-ball, where they are expanded, 

 to form the retina. 



3d pair. Nervi motores oculorum ; 

 arise from the crura cerebri, and are dis- 

 tributed to some of the muscles of the 

 eye-ball. 



4th pair. Nervi trochleares ; come from 

 the valve of the brain, and supply the 

 trochlearis muscle of the eye. 



5th pair. Nervi trigemini ; arise from 

 the side of the medulla oblongata. This 

 nerve divides into three branches, of 

 which the first, or ophthalmic, goes into 

 the orbit, and after giving a few branches 

 there passes out on the forehead. The 

 second, or superior maxillary, supplies the 

 parts about the upper jaw; a remarkable 

 branch of it is the infra-orbital, which 

 comes through the large hole under the 

 orbit to the face. The third, or inferior 

 maxillary, is distributed to the lower jaw 

 and adjacent parts. 



6th pair. Nervi motores externi ; from 

 the medulla oblongata to the external 

 straight muscle of the eye. 



7th pair. Nervi auditorii. This pair 

 consists of two nerves lying in contact, 

 but completely distinct from each other, 

 both in their origin, course, and distribu- 

 tion. The porlio mollis of this nerve is 



distributed to the labyrinth of the 'eat'. 

 The portio dura goes through the tempo- 

 ral bone, and is very widely spread over 

 the face. These nerves are more cor- 

 rectly termed nervus auditorius, and ner~ 

 vus facialis. The chorda tympani is a 

 branch of communication between the fa- 

 cial nerve and the lingual branch of the 

 inferior maxillary. 



8th pair. Par vagum ; arises from the 

 medulla spinalis, before it quits the cra- 

 nium. It receives an accessory branch, 

 that originates from the upper portion of" 

 the medulla spinalis, contained in the cer- 

 vical vertebrae. The par vagum passes 

 along the neck, in company with the ca- 

 rotid artery and the internal jugular vein, 

 It sends oft'in the upper part of the neck, 

 1. the glossopharyngeal nerve ; 2. supe- 

 rior laryngeal ; and 3. the accessory 

 branch ; the trunk that enters the chest, 

 and gives rise to the inferior laryngeal or 

 recurrent nerve. It afterwards becomes 

 connected to the oesophagus, and passes 

 the diaphragm in conjunction with that 

 tube, to be distributed finally to the sto- 

 mach ; sending in its passage several 

 brandies which supply the lungs. 



9th pair. Nervi linguales; arise near 

 the former, go through the foramen con- 

 dyloideum, and supply the muscles of the 

 tongue. 



Nerves of the medulla spinalis. The cer- 

 vical nerves, soon after they come out 

 from between the vertebrae, communicate 

 with each other. They supply all the mus- 

 cles which are situated about the verte- 

 brae of the neck. The second sends a large 

 branch, which ramifies extensively over 

 the occiput. 



The nerve of the diaphragm, called the 

 phrenic or diaphragmatic, arises princi- 

 pally from the fourth cervical nerve. It 

 lies close on the anterior scalenus muscle* 

 then goes over the pericardium to the 

 diaphragm. 



The four lower cervical nerves, and the 

 first dorsal, concur in forming the axillary 

 plexus, from which the upper extremity 

 derives its supply. These are- large ner- 

 vous trunks coming out at the side of the 

 neck, and variously united to each other, 

 They go behind the clavicle with the axil- 

 lary artery. This plexus sends off the 

 following branches : 



1. Nervi thoracici, accompanying the 

 thoracic arteries. 



2. Nervus supra-scapularis, distributed 

 with the artery of the same name. 



3. Nervus axillaris, following the 

 course of the posterior circumflex artery. 



4. CutruieusJ interims, running over the 



