NEUROLOGY. 143 



in number, usually four, and sometimes only three, and often one is prolon- 

 gated into another. The external branches of each are two, communicating ; 

 they accompany the lumbar arteries, beneath the psoas muscle, close to the 

 grooves on the sides of the vertebrae, and join the anterior lumbar nerves 

 in the intervertebral foramina; they are white and distinct, and may be re- 

 garded as the lumbar roots of the sympathetic. These branches frequently 

 have ganglions upon them, and they often unite with filaments from the 

 lumbar plexus. 



The anterior and internal branches are aortic and splanchnic. The aortic 

 branches are numerous ; they pass forwards in front of the aorta ; the nerves 

 of opposite sides unite, and are joined by branches from the solar plexus, 

 and form a plexus, lumbo-aortic. This surrounds the aorta between the su- 

 perior and inferior mesenteric arteries ; small arteries and lymphatic glands 

 and vessels are entangled in it ; some of its branches join the inferior me- 

 senteric plexus ; inferiorly it divides into three portions ; the middle enters 

 the pelvis, and joins the hypogastric plexus ; the lateral accompany the 

 common iliac arteries to their division, and several filaments are prolonged 

 around the internal and external iliac vessels. The splanchnic branches 

 pass forwards from each ganglion, and join the several abdominal plexuses 

 already mentioned. 



The hypogastric plexibs is of considerable "extent ; it is formed by the con- 

 tinuation of the lumbo-aortic plexus, joined by filaments from the lumbar 

 ganglions ; is situated in front of the base of the sacrum, between the com- 

 mon iliac arteries, and divides into a right and left hypogastric plexus; each 

 of these is joined by branches from the sacral ganglions and anterior sacral 

 spinal nerves ; each plexus sends off numerous branches, which again form 

 secondary plexuses on the organs to which they are distributed. Thus we 

 have hemorrhoidal, vesical, prostatic, vesicular, ovarian, and uterine plex- 

 uses. All these plexuses contain filaments from the sacral nerves, as well 

 as from the sympathetic, and all are conducted to their terminations by the 

 arteries of each organ. 



As the sympathetic cords descend obliquely inwards, over the base of the 

 sacrum, behind the iliac vessels, they are extremely small; in the" pelvis, 

 they at first increase in size, descend converging, and each ends in a minute 

 thread; they are placed near the inner margin of the anterior sacral foramina. 

 The sacral ganglions are four or five in number, of an oval or round form ; 

 their external branches ]om the anterior sacral nerves ; their internal branches 

 join 'the hypogastric, or some of their secondary plexuses. From the last 

 ganglion a small branch arches across to meet a similar one from the oppo- 

 site side : on this a small ganglion (impar) is occasionally to be found ; if 

 absent, a connecting plexus occupies its place ; the terminal filaments are 

 very minute, and distributed to the fore part of the os coccyx. 



Although the sympathetic nerves and their branches appear to differ in 

 structure from the cerebro-spinal nerves, yet they are essentially the same ; 

 the fibres seldom appear so white, but have rather a greyish-red color. 

 The general neurilemma of each nerve is more dense, and therefore the 

 internal fibrous or fasciculated texture is not so obvious ; but if the former 



ICONOGRAPHIC ENCYCLOPAEDIA. VOL. 11. 54 849 



