ELEMENTAEY DEMONSTRATIONS 



153 



stimulated point. The contraction preceded by the dilatation slowly 

 passes as a peristaltic wave down the intestine and pushes the bolus 

 onwards. This peristalsis can be excited after section of both 

 splanchnic and vagus nerves, but not after injecting nicotine or 

 painting the intestine with cocaine. It is a co-ordinated reflex carried 

 out by the peripheral nervous mechanism Auerbach's plexus (Bayliss 

 and Starling). 



The small intestine receives nerve-fibres from the splanchnics which 

 pass through the semilunar and superior mesen- 

 teric ganglia, and along the mesenteric arteries. 

 It also receives fibres from the vagi 

 the continuation of the right vagus. The 

 splanchnic nerve inhibits the intestine, while . 



ing peristaltic contraction 



excitation of the vagus after injection of atropin of intestine. 



(to paralyse the cardiac inhibiting fibres) augments the tone and swaying 



movements. 



The colon receives fibres from inferior mesenteric ganglia via the 

 lower dorsal and upper lumbar nerves, and from the second and third 

 sacral nerves (pelvic nerves). The former inhibit and the latter 

 augment the movements. 



Fio. 135. Diagram show- 



CHAPTER XLIIL 

 SALIVARY SECRETION. 



Salivary Secretion. The submaxillary gland is situated within and 

 a little behind the posterior angle of the lower jaw bone. 



The animal anaesthetised with ether and chloroform is placed on 

 its back, and its head extended. An incision is then made along the 

 internal border of the jaw bone. The internal border of the digastric 

 muscle is thus exposed. This is pulled aside by a hook so as to expose 

 the transverse fibres of the mylohyoid muscles. 



The mylohyoid is carefully severed following the line of the digastric 

 muscle. The submaxillary and sublingual ducts crossed by the lingual 

 nerve are now exposed in the depth of the wound. Wharton's duct 

 is the larger and external to the sublingual duct. Just where the lingual 

 nerve crosses the ducts it gives off a small branch the chorda 

 tympani. In the angle formed by the origin of the chorda tympani 

 from the lingual nerve there lies the sublingual ganglion (it is erroneous 

 to term this ganglion "submaxillary"). A ligature^is placed beneath 

 the lingual nerve central to the origin of the chorda tympani, and the 

 lingual nerve is divided central to the ligature. Two ligatures are 



