I3i6 



A MANUAL OF ANATOMY 



a spinal nerve, which is necessarily a mixed nerve, inasmuch as it 

 is composed of afferent and efferent fibres. 



Each spinal nerve breaks up into an anterior and a posterior 

 primary division. 



The upper cervical nerve - roots are short, and pass almost 

 horizontally outwards. The succeeding nerve-roots, however, 

 gradually increase in length, and incline downwards as they pass 

 outwards. This downward inclination goes on increasing until 

 it becomes almost vertical in the case of the limibar, sacral, and 



Fig. 550. — Two Segments of the Spinal Cord, showing the Attach- 

 ments OF the Anterior and Posterior Nerve-Roots, and thb 

 Spinal Ganglia. 



A, Superior View ; B, Anterior View. 



1, I. Anterior Median Fissure 5, 5. Spinal Ganglion 



2, 2. Posterior Median Fissure 6, 6. Spinal Nerve 



3, 3. Anterior or Motor Nerve-Root 7, 7. Anterior Primary Division 



4, 4. Posterior or Sensory Nerve-Root 8, 8. Posterior Primary Division 



9, 9. External and Internal Branches of Posterior Primary Division 



coccygeal nerves, which constitute the cauda equina. From this 

 disposition it follows that, in the majority of cases, the superficial 

 origins of the spinal nerves art on a higher level than the inter- 

 vertebral foramina through which they emerge from the spinal 

 canal. 



Relation of the Spines of Vertebrae to the Bodies and to the Origins of the 

 Nerves. — In the case of the cervical and the eleventh and twelfth thoracic 

 vertebra; the extremities of the spinous processes correspond to the lower 

 margins of the bodies of the respective vertebrae. In the case of the thoracic- 

 vertebrae, from the first to the tenth inclusive, the extremity of each spinous, 

 process corresponds to the upper margin of the body immediately below. 

 In the case of the lumbar vertebra; the extremity of each spinous process 

 corresponds to the centre of the body of its own vertebra. 



Each cervical spinous process is nearly opposite the lower fasciculi of the 

 roots of the nerve below. The spinous process of the seventh cervical vertebraj 



