208 THE SURGICAL PHYSIOLOGY 



next, including the region of the patella, is the third 

 lumbar. The small sciatic nerve area corresponds to 

 the second sacral, and the internal saphenous nerve 

 area to the fourth lumbar segment. 



With regard to motor distribution, the fifth cervical 

 supplies the deltoid +biceps+supinator longus group, 

 as well as the dorsal scapular muscles and rhomboids. 

 In infantile palsy and other anterior horn or nerve- 

 root affections, these muscles may be found paralysed 

 and atrophied in company. On the other hand, a 

 fracture of the spine irritating this segment brings 

 about a characteristic position of the arms 'V . The 

 first dorsal gives off sympathetic branches dilating 

 the pupil. 



The anatomy of the lumbo-sacral plexus makes it 

 easy to remember that the quadriceps and adductors 

 must be supplied from the lumbar nerves, whereas the 

 hamstrings and crural muscles are innervated from the 

 sciatic roots. There is a general tendency for flexors 

 to derive their nerve supply from a level slightly 

 below that for the extensors. It is easy to see 

 why this should be the case if we glance at a 

 quadruped, where the flexors are posterior to the 

 extensors. 



Flaccid paralysis and anaesthesia of the lower limbs, 

 with sphincter trouble, may be due to a tumour 

 growing either in the cauda equina or in the conus 

 medullaris of the cord itself. The diagnosis is often 

 difficult, but tumours of the cauda are usually 

 characterized by a slower course, asymmetry, very 

 violent pain, and Lasegne's sign — pain on flexing the 

 thigh and thus pulhng on the nerve-roots. Operative 



