160 PRACTICAL PHYSIOLOGY 



It is a secretory nerve to the gastric glands and pancreas. 



It contains afferent fibres from the heart which provoke reflex 

 movements, pressor or depressor effects, and reflex cardiac inhibition. 



The afferent fibres of the vagus coming from the lungs regulate the 

 rhythm of respiration. 



The superior laryngeal branch of the vagus is the motor nerve to 

 the crico-thyroid muscles and the sensory to the larynx. 



The inferior laryngeal branch is the motor nerve to the intrinsic 

 muscles of the larynx. 



Spinal Preparation of Mammal. Sherrington employs the following 

 preparation for studying blood pressure and spinal reflexes, action 

 of vagus on heart, oncometry of kidney, action of nerves of 

 bladder, etc. : 



The animal (cat) being deeply anaesthetised with chloroform, a 

 cannula is inserted into the trachea. Both common carotids are 

 ligated. A transverse incision through the skin is made over the 

 occiput and extended laterally close behind the pinnae. The skin is 

 retracted backwards so as to expose the neck muscles at the level of 

 the axis vertebra. The ends of the transverse processes of the atlas 

 are then felt for and a deep incision made through the muscu- 

 lature just behind these processes. The large spinous process of 

 the axis is notched with the bone forceps. A strong thick ligature is 

 passed by a sharp-ended aneurism needle close under the body of 

 the axis and is tied tightly in the groove left by the incision behind 

 the transverse processes of the atlas and the notch made in the 

 spinous process of the axis. This compresses the vertebral arteries 

 where they pass from transverse process of axis to transverse process of 

 atlas. A second strong ligature is then looped round the neck at the 

 level of the cricoid and is so passed as to include the whole neck 

 except the trachea. Decapitation is then performed with an ampu- 

 tating knife passed from the ventral aspect of the neck through 

 the occipito-atlantal space, severing the cord just behind its junction 

 with the bulb. The ligature round the neck is drawn tight at the 

 moment of decapitation. The severed head of the deeply narcotised 

 animal is then destroyed. Haemorrhage is extremely slight. If there is 

 oozing from the vertebral canal it is arrested by raising the neck 

 somewhat above the rest of the carcase. The carcase is placed on 

 a small metal-topped table warmed by an electric lamp below. 

 Artificial respiration is employed to ventilate the lungs, the fresh air 

 supplied from the bellows being warmed by passing through a chamber 

 containing a small electric lamp. The skin flaps are stitched together, 

 covering the exposed end of the spinal cord and other structures bared 



