904 



THE NERVOUS SYSTEM 



Third thoracic 

 Fourth " 



Fifth " 



Sixth " 

 Seventh " 



Eighth " 



(A) Just above middle of spine of seventh cervical vertebra. 



(B) Lower border of spine of second thoracic vertebra. 



(A) Just below upper border of spine of first thoracic vertebra. 



(B) Junction of upper third and lower two-thirds of spine of third thoracic 



vertebra. 



(A) Upper border of spine of second thoracic vertebra. 



(B) Junction of upper quarter and lower three-quarters of spine of fourth 



thoracic vertebra. 



(A) Lower borderof spine of second thoracic vertebra. 



(B) Just below upper border of spine of fifth thoracic vertebra. 



(A) Junction of upper third and lower two-thirds of spine of fourth thoracic 



vertebra. 



(B) Just above lower border of spine of fifth thoracic vertebra. 



(A) Junction of upper two-thirds and lower third of interval between spines 



of fourth thoracic and fifth thoracic vertebra. 



(B) Junction of upper quarter and lower three-quarters of spine of t 



thoracic vertebra. 



(A) Midway between spines of fifth thoracic and sixth thoracic vertebra. 



(B) Upper border of spine of seventh thoracic vertebra. 



(A) Midway between spines of sixth thoracic and seventh thoracic vertebra. 



(B) Middle of the spine of eighth thoracic vertebra. 



(A) Junction of upper quarter and lower three-quarters of spine of seventh 



thoracic vertebra. 



(B) Just above spine of ninth thoracic vertebra. 



(A) Junction of upper quarter and lower three-quarters of spine of eighth 



thoracic vertebra. 



(B) Just below spine of ninth thoracic vertebra. 



(A) Midway between spines of eighth thoracic and ninth thoracic vertebra;. 



(B) Lower border of spine of tenth thoracic vertebra. 



(A) Middle of spine of ninth thoracic vertebra. 



(B) Junction of upper third and lower two-thirds of spine of eleventh thoracic 



vertebra. 



(A) Middle of spine of tenth thoracic vertebra. 



(B) Just below spine of eleventh thoracic vertebra. 



(A) Just below spine of tenth thoracic vertebra. 



(B) Junction of upper quarter and lower three-quarters of spine of twelfth 



thoracic vertebra. 



(A) Junction of upper third and lower two-thirds of spine of eleventh thoracic 



vertebra. 



(B) Middle of spine of twelfth thoracic vertebra. 



(A) Just above lower border of spine of eleventh thoracic vertebra. 



(B) Lower border of spine of first lumbar vertebra. 



(A) Lower border of spine of first lumbar vertebra. 



(B) Just below upper border of spine of second lumbar vertebra. 



Relative size of the nerves. The sizeof the different spinal nerves varies greatly. 

 Just as the spinal cord shows marked enlargements in the cervical and lumbar 

 regions necessitated by the greater amount of innervation required of these regions 

 for the structures of the upper and lower limbs, so the nerves attached to these regions 

 are considerably larger than elsewhere. The smaller nerves are found in the two 

 extremities of the series and in the mid-thoracic region. The smallest nerve is the 

 coccygeal, and the next in order of size are the lower sacral and the first two or three 

 cervical nerves. The largest nerves are those which contribute most to the great 

 nerve-trunks for the innervation of the skin and muscles of the limbs: the lower 

 cervical and first thoracic for the upper limbs and the lower lumbar and first sacral 

 for the lower limbs. The nerves gradually increase in the series in passing from the 

 smaller towards the larger. 



The primary divisions of the nerve-trunk. A typical spinal nerve (middle 

 thoracic, for example), just as it emerges from the intervertebral foramen, divides 

 into four branches: the two large primary divisions; viz., the posterior primary 

 division (ramus posterior) and the anterior primary division (ramus anterior) ; 

 third, the small ramus communicans, by which it is connected with the sympathetic : 

 and fourth, the smaller, ramus meningeus (recurrent branch), which immediately 

 turns centralwards for the innervation of the membranes of the spinal cord. 



In general, the posterior primary division passes dorsalwards between the arches 

 or transverse processes of the two adjacent vertebra- in relation with the anterior 

 costo-transverse ligament, and then divides (with the exception of the first cervical, 



Tenth " 

 Eleventh " 



Twelfth " 



First lumbar 

 Second " 



Third " 

 Fourth " 



Fifth " 



First sacral 

 Fifth " 

 Coccygeal 



