364 COMPARATIVE ZOOLOGY OF CHORDATES 



These muscles are striated and voluntary. In order that such 

 movements may be properly coordinated, the animal must 

 have some information (unconscious, of course) of the existing 

 state of its muscles, tendons, and joints. This is supplied by 

 sense-organs which are situated in these structures, and are 

 called proprioceptors. 



At the same time, there is a " world " within the animal, 

 and sensations arise from stimuli which start from organs 



X 



da 



amg-l-p 



-ama. 



Fig. 169. — Diagrammatic transverse section through the trunk of a verte- 

 brate showing the relations of the nerve-roots, sympathetic ganglia, 

 and the functional components. 



ama, anterior mesenteric artery ; amg, anterior mesenteric ganglion ; 

 da, dorsal aorta ; dr, dorsal nerve-root ; g, gut ; n, notochord ; re, ramus 

 communicans ; sg, spinal ganglion ; sm, somatic motor region of grey 

 matter ; ss, somatic sensory region ; sy, sympathetic ganglion ; vm, visceral 

 motor region ; vr, ventral nerve-root ; vs, visceral sensory region. 



such as the stomach, intestine, or bladder, and the functions 

 connected with them. The sense-organs of taste are largely 

 of use in connexion with what is about to enter the alimentary 

 canal, and they also belong here. Such sense organs are called 

 interoceptors. The reactions to these stimuli take the form of 

 secretions on the part of glands, and contractions of the 

 muscles of the alimentary canal, bladder, arteries, or oviduct. 

 Such muscles are always smooth and involuntary. 



