300 ANATOMY OF THE DOMESTIC FOWL 



The anterior portion gives off an anterior splanchnic nerve, or 

 plexus (Fig. 64, No. 43) which accompanies the celiac axial artery 

 to the gizzard and Hver, communicating with the pneumogastric. 

 The posterior splanchnic nerve is intimately combined with the 

 adrenal body, and the testes, or the ovary (Fig. 64, No. 45). Intes- 

 tinal branches accompany those of the mesenteric arteries (Fig. 64, 

 No. 46). Other branches supply the kidneys, and communicate 

 with long branches of the spinal nerves destined for the cloaca and 

 adjacent parts,' and thus form a plexus similar to that found in 

 mammals. 



FUNCTIONS OF THE NERVOUS SYSTEM 



According to function, the nerves composing the trunks are 

 divided into afferent and efferent. 



The afferent nerves are those that convey the impulses from the 

 periphery of the body to the nerve center, which are located in the 

 brain or in the spinal cord. The impulses conveyed are those of 

 special senses, as sight, hearing, taste, touch, and smell. Impulses 

 producing sensation pleasurable or painful cOme from the skin, the 

 muscle, or the viscera. 



The efferent nerves are those which convey impulses from the 

 nerve centers to the periphery. These impulses may be motor as 

 those going to the muscle cells of the skeletal muscles, the viscera, 

 or the blood-vessels. These motor impvilses make movements in 

 these organs possible. In the blood-vessel they result in the control 

 of the caUber of the vessel. These impulses may be of an inhibitory 

 character, as in slowing the heart. They may be secretory impulses 

 stimulating the gland to activity or regulating metabolism. 



The ganglia are nerve centers which receive and generate im- 

 pulses; the nerve trunks are filaments which convey impulses. The 

 gray matter of the cord described above is the ganglionic portion, 

 and the outer white matter is made up of nerve fibers which convey 

 impulses from one part of the cord to another, or to and from the 

 brain. 



The nerves that have their roots in the spinal cord superiorly, 

 are sensory; that is, they convey the sensory impulses from the 

 periphery to the cord gangUon and to the brain. They have a 

 ganglion just outside the cord. 



The nerves that have their roots in the spinal cord inferiorly; 

 that is, they convey motor impulses from the nerve centers to the 



