chordo tympani branch parotid salivary gland 

 sphenopalatine ganglion palatine^ tympanic plexus 



ciliary ganglion \ ,,, I* 'i ''2,3 



lacrimal 

 gland 



eye 



part of sympathetic chain (including stellate ganglion) left ouf 

 nuclei in spinal cord 

 thoracics (lumbar outflow) sacral outflow 



. ■■■ I- submaxillary 



submaxillory salivary ,. ' 



' . _, ' ganglion 

 gland 



otic ganglion 



bladder sphincter 

 bladder 



superior mesenteric ganglion 

 Figure 13-3. Autonomic system of the tetrapod. (After Goodrich, 1930) 



lature of the third arch (hyoid), and the parotid sahvary 

 gland. 



The vagus nerve (X) is composed of several components 

 which appear to be comparable to the spinal nerves behind 

 the brain area. This nerve like the facial is largely sensory and, 

 in lower forms, related to the lateral-line system, which will 

 be described later. It also has motor components serving the 

 arch muscles of the branchial region. It extends into the 

 body cavity as an element of the parasympathetic system 

 supplying most of the visceral organs. The root of this 

 nerve is associated with two large ganglia, a proximal jugu- 

 lar and a more distal nodose ganglion. 



The spinal accessory nerve (XI) arises in association 

 with the vagus, and is composed primarily of motor fibers 

 distributed to the muscles of the pharynx and larynx (also 

 the sternocleidomastoid and trapezius muscles). The more 

 posterior roots enter the skull through the foramen magnum. 

 The separation of an eleventh nerve from the tenth appears 

 to be a characteristic of the amniotes. 



The hypoglossal nerve (XII) arises from a large number of 

 roots of spinal origin. The fibers arise from motor neurons 

 in the myelencephalon and the anterior part of the spinal 

 cord, ventral to the roots of the vagus. The trunk leaves the 

 skull with the vagus and innervates the hypoglossal muscles 

 of the tongue. 



The peripheral artd autonomic sysfems The typical segmen- 

 tal nerve is that of the spinal cord. Each has a dorsal root 

 (with a sensory ganglion) and a ventral root. The senson,' 

 ganglion is derived from neural crest cells. Processes from 



these cells grow into the spinal cord, where they synapse, 

 and outward along with fibers from motor neurons of the 

 ventral horn to form the spinal nerve and its branches. 



The cranial nerves develop similarly. The motor elements 

 grow out from their nuclei; the sensory ganglia arise from 

 neural-crest cells along with contributions from epibran- 

 chial placodes (ectodermal thickenings which sink into 

 the underlying tissues) in the cases of V, VII (including 

 VIII), IX, and X. 



The autonomic system plays a role in the vegetative 

 functioning (internal maintenance) of the body. It is made 

 up of two basic divisions; parasympathetic and sympathetic 

 which reciprocally innervate each visceral organ (Figure 

 13-3). Where one stimulates, the other inhibits. The auto- 

 nomic system has both sensory and motor elements but 

 primarily consists of the latter. The segmental sympathetic 

 ganglia (housing motor neurons) and the plexuses asso- 

 ciated with the gut (cardiac, coeliac, hypogastric) are of 

 neurai-crest origin; the crest cells migrate out along the de- 

 veloping spinal nerves. Some of motor elements and the 

 sensory components are of spinal origin. The plexuses of the 

 gut wall (Meissner's and Auerbach's) arise from cells mi- 

 grating along the path of the vagus nerve and along other 

 visceral nerves. 



Reptiles 



The brain of the lizard is quite similar to that of the 

 mammal but has a smooth cerebral surface (Figure 13-4). 

 Histologically the cerebrum is different. The neopallium 



THE CONDUCTING AND INTEGRATING SYSTEM • 387 



