6 THORAX 



either both sets of fibres or only one or the other set. 

 Eventually, however, the peripheral parts of the fibres con- 

 veying impulses from and those conveying impulses to the 

 spinal medulla separate from one another. The fibres which 

 convey impulses from the spinal medulla become the motor 

 nerves which end in the muscle fibres, whilst the fibres which 



Medial cutaneous branch of medial division of posterior ramus 



Lateral cutaneous branch of medial division of posterior ramus 



Lateral division of posterior ramus dividing 



into terminal muscular branches' N 



Posterior ramus 

 Anterior ramus x 



Muscular branches 



Posterior cutaneous 



branch of lateral 



division of 



anterior ramus 



Latera division of 

 anterior ramus 



Anterior cutaneous 



branch of lateral 



division of 



anterior ramus 



Sympathetic gangl 

 Anterior division of anterior ramus 



. Medial division of 



! ^_ ^ posterior ramus 



- Posterior ganglionated 



root 



Posterior funiculus of 

 ' spinal medulla 



Posterior grey column 



Antero-lateral 

 funiculus 

 Anterior grey 

 column 



Medial cutaneous branch of anterior 

 division of anterior ramus 



Lateral cutaneous branch of anterior division of anterior ramus 



FIG. 2. Diagram of the Spinal Nerve. Note that the medial division of 

 the posterior ramus is represented as distributed to skin, whilst the lateral 

 division terminates at a deeper level in muscle ; in some situations the 

 reverse condition occurs. The medial and lateral divisions of all 

 posterior rami supply muscles. 



convey sensory impulses only are the sensory nerve fibres. 

 The sensory nerve fibres which convey sensory impulses from 

 the skin are termed cutaneous nerves. 



In the region of the thorax the branches which become 



