296 PRACTICAL ANATOMY. 



projectiles. The nerves to and from the brain are media by which the impres- 

 sions travel. These impressions, then, and the nerves by which they travel, are 

 projectiles, and are amenable to the law of philosophy governing all projectiles : 

 ( i ) A projectile follows the line of least resistance ; (2) a projectile follows the 

 point of greatest traction ; (3) a projectile may follow the resultant of these two 

 /. c., the line of greatest traction and the point of least resistance. 



Anatomical factors determining the above are simply the amount and kind 

 of nerve distribution at the locality whence the reflex proceeds. On this hypo- 

 thesis alone do we account for the reference of both pain and motion, in their 

 logical places, in simplex reflexes. In figure ] 87, a simple reflex, the logical 

 place for the pain is the conjunctiva; the logical place for the motion is in the 

 orbicularis palpebrarum. Here the influences, sensory and motor, follow the 

 greatest direct nerve distribution over cranial nerves having maximal ability 

 to transmit both sensation and motion. On this hypothesis do we account for 

 pain, the result of an irritant, for example, in the ovary, rectum, or uterus, not 

 in its logical place in the organ itself, but in its illogical place, far away in some 

 other part of the body, where both reflex pain and reflex motion may be the 

 symptoms. These are complex reflexes ; still, just as logical in every way and 

 just as amenable to the law of projectiles as simple reflexes. (Fig. 185.) 



Pain is diagnosticaily one of the most important subjective symptoms. It is 

 reported peripherally. You must, then, have a thorough knowledge of the 

 cutaneous and membranous distribution of somatic nerves, since it is through 

 these nerves that pain from every organ in the body may make its demurrer. The 

 steps, then, anatomically, in tracing pain for diagnostic purposes are : 



1 . What cutaneous or sensory nerves supply the part ? 



2. Of what mixed nerve or plexus are they a part ? 



3. Where do these mixed nerves leave the spinal canal ? 



4. Do they correspond to the six upper intercostals ? 



5. Do they correspond to the six lower intercostals ? 



6. Do they correspond to the cervical plexus ? 



7. Do they correspond to the brachial plexus ? 



8. Do they correspond to the lumbar plexus ? 



9. Do they correspond to the sacral plexus ? 



10. What territory of organs does the hypogastric plexus supply ? 



i i . What territory does the solar plexus supply ? 



12. What territory does the cardiac plexus supply? 



Any considerable pain, then, as previously stated, is reported by a somatic 

 nerve. If this somatic nerve is the innervation pure and simple of the painful 

 part under consideration, then the pain is a simple direct pain. If, however, 

 as frequently happens, the somatic nerve is the medium through which vast 

 territories are made to suffer, while the exciting cause is in some remote organ, 

 then this pain is a reflex pain. The somatic nerves may also produce reflex 

 muscular movements in the muscles corresponding to the region of the pain. 

 (See page 264.) 



The student can not become too well grounded in the philosophical distribu- 

 tion of a mixed nerve : The nerve-trunk that supplies a group of muscles sup- 

 plies also the skin covering those muscles ; the articulation that these muscles 

 move ; the serous or synovial membrane in contact with which these muscles 

 may lie. The six upper intercostal nerves supply, then, not only intercostal 

 muscles, but the pleura as well ; the six lower supply not only the muscles of 

 the abdominal walls, but the peritoneum also. An organ, then, having a sym- 

 pathetic nerve-supply, may manifest its pain either in skin, membranes, or articu- 

 lations, and still not transcend the logic of the law of reflex phenomena. 



