2 3 o THE DIGESTIVE SYSTEiM 



are innervated by different cerebral nerves. The fifth nerve 

 is involved in closing the mouth ; the seventh, in compressing 

 the lips and cheeks; the ninth, in elevating the larynx; the 

 tenth and eleventh, in elevating the soft palate, in closing the 

 larynx, in approximating the palatine arches and in urging the 

 bolus onwards to the oesophagus ; the twelfth, in elevating the 

 tongue. Paralysis of any one of the nerves involved causes 

 an appreciable disturbance only when the lesion is bilateral, 

 and the act of deglutition is interfered with most in lesions of 

 the ninth, tenth and eleventh nerves (Bulbar Paralysis, p. 108). 



The (Esophagus is a muscular tube which begins in the 

 neck at the level of the cricoid cartilage sixth cervical 

 vertebra where it is continuous with the laryngeal part of 

 the pharynx. It passes down through the thorax, pierces the 

 diaphragm and terminates in the abdomen by becoming 

 continuous with the stomach. 



In the neck, the oesophagus lies in front of the vertebral 

 column, and, when it is obstructed or compressed against the 

 bone in this region, swallowing becomes impossible, the food 

 being rejected at once. Anteriorly, it is related to the trachea 

 and the recurrent nerves (Fig. 50), while it is overlapped by 

 the posterior borders of the lobes of the thyreoid gland. 

 In the lower part of the neck, the thoracic duct is related to 

 its left border. Enlargement of the thyreoid gland may cause 

 dysphagia secondarily to dyspnoea (Fig. 50), but the condition 

 is rarely met with in practice. 



In the thorax^ the oesophagus continues its course down- 

 wards in front of the vertebral column. In the upper part, it 

 is placed behind the trachea and is crossed by the arch of the 

 aorta (Fig. 113) and the left bronchus. In the lower part of the 

 thorax, the oesophagus deviates slightly to the left and, as it 

 passes through the diaphragm, it lies one inch from the median 

 plane. As it descends, it lies behind the pericardial sac, and 

 as a result of this relationship, swallowing causes pain in the 

 presence of pericarditis (p. 289). 



The cesophageal opening is placed in the muscular part of 



