CHAP. IX.] XEEVOUS SY^'^TEM AND ORGANS OF SENSE. 277 



cornu, and some cross the posterior commissure and rcacli the 

 posterior and lateral columns of the opposite side. 



The funiculi of the anterior (ventral) root pass straight to the 

 anterior cornu and there also diverge postaxially, preaxially, and 

 horizontally. 



The funiculi of the posterior (dorsal) root unite to form a single 

 cord, which is furnished with an oval mass of grey matter, or 

 ganglion, varying in size with the size of the nerve. 



The funiculi of the anterior (ventral) root unite together without 

 developing any ganglion, and the cord so formed unites with that 

 from the posterior root beyond {i.e., distally to) the ganglion. 



Each spinal nerve having thus been formed by the union of its 

 roots, divides (as before said) into two conspicuous branches termed 

 its DORSAL and ventral primary divisions. Fibres from each of 

 the two roots are so blended in the part where the nerve is single, that 

 after its division each of its two parts contain fibres derived from both 

 the anterior (ventral) and posterior (dorsal) root of the nerve. 



The DORSAL PRIMARY I3IVISI0NS of the Spinal nerves are dis- 

 tributed to the muscles and skin of the dorsal region, and divide into 

 internal and external branches. 



The cervical internal branches pass upwards in the vicinity of the 

 neural arches. The external branches pass outwards, and supply 

 the cer'sacal prolongations of the erector spinee. 



The dorsal internal branches proceed between the multifidus 

 spina?, and either the semi-spinalis dorsi or the longissimus dorsi — 

 therefore in the vicinity of the neural arches. Their external 

 branches (which become bigger from before backwards) pass be- 

 neath the longissimus dorsi to the interval between it and the 

 sacro-lumbalis or its continuation forwards. 



The lumbar internal branches pass baclcAvards close to the zyg- 

 apophyses into the multifidus spinfo, therefore close (once more) to 

 the neural arches. Their external branches enter the erector spina?, 

 which represents the longissimus dorsi and sacro-lumbalis un- 

 differentiated. 



The sacral external and internal branches are distributed iu an 

 analogous manner. 



The VENTRAL PRIMARY DIVISIONS of the Spinal nerves are dis- 

 tributed to the more ventrally situated parts of the body, and they 

 are generally a good deal larger than are the dorsal primary di\asions. 

 They do not divide into an internal and external branch as do the 

 dorsal primary divisions of the spinal nerves, but they tend to unite 

 together in sundry ^;/t^r^^se.s, and each gives off a minute branch 

 inwards to the sympathetic system, and thus in a certain sense even 

 these anterior primary divisions bifurcate ; they bifurcate, namely, 

 into a large outer division, and a minute inner one going to the 

 sympathetic. 



The ventral primary divisions of the cervical nerves pass out- 

 Avards between the scaleni and the rectus anticus major muscles. 



The first four or five form an interlacement called the cervical 



