CHAP. XXI.] THE ABDOMINAL PLEXUSES. 141 



The branches of this plexus which pass between the laminae of 

 the mesentery do not accompany the smaller branches of the artery 

 so closely as elsewhere. They anastomose by arches, from which 

 small branches pass to the intestine. The precise mode of termi- 

 nation of these nerves in the tunics of the intestines has not been 

 ascertained. 



In the pelvis we find a remarkably complicated plexiform arrange- 

 ment of nerves distributed to the viscera of that cavity. These 

 nerves are derived from the hypogastric, and from the inferior me- 

 senteric (p. 138), and receive many fibres from the sacral nerves, 

 which latter fibres are principally distributed to the pelvic plexus, 

 a name given by Mr. Beck to an intricate anastomosis of nerves and 

 small ganglia distributed to the rectum, bladder and vagina. This 

 plexus derives its nerves from the lower part of the hypogastric 

 plexus, and from the branches of the sacral plexus. 



A very important peculiarity of all the plexuses, wherever found, 

 of the sympathetic nerve, consists in the presence of a quantity 

 of vesicular matter in them, deposited in ganglia of very variable 

 size, sometimes extremely minute, very rarely of great size, which 

 are found scattered amongst them. These ganglia appear to give 

 origin to gelatinous fibres. The plexuses, therefore, have the double 

 office of intermingling fibres from different sources, and of affording 

 points of origin for new nerve fibres. 



Function of the Sympathetic Nerve. In considering the function 

 of this portion of the nervous system, it is of the utmost importance 

 to pay close attention to the facts which the anatomical analysis of 

 it discloses. 



These facts are, that it contains a vast number of centres to and 

 from which nerves proceed, and in which, it may be stated almost 

 with certainty, gelatinous fibres originate : that in nearly every 

 part of it two kinds of fibres exist, the gelatinous and the tubular ; 

 that the tubular are derived from the cerebro-spinal centre, the 

 gelatinous from the sympathetic ganglia. 



Two questions are to be solved in reference to the sympathetic. 



1. Is the sympathetic a distinct and independent portion of the 

 nervous system ? or is it merely an off-shoot from the brain and 

 spinal cord, exhibiting certain peculiarities of arrangement ? 



2. Do its fibres exhibit the same powers as those of cerebro-spinal 

 nerves? that is, are they sensitive and motor? 



I. No physiological question has been more amply discussed of 

 late years than that of the relation of the sympathetic to the cerebro- 

 spinal centres. 



