THE PHARYNX. 



445 



corna of tlie os hyoides, or styloid bone, instead of its upper part ; its fibres pass 

 beneath the hyo- and thyro-hyoideus muscles, and proceed upwards in crossinsr 

 the direction of the precedin<^ muscle, terminating on the middle raphe on the 

 superior face. It pulls the upper wall of the pharynx backwards and downwards. 



Certain anatomists designate it the inferior stylo-pharyngeus, and consider it 

 as a constrictor of the pharynx. It sometimes exist only on one side. 



3. Vessels and nerves. — The blood sent to the pharynx comes from the 

 pharyngeal and thijroideal arteries. The nerves are supplied by the glosso- 

 pharytnjeus, pnenmogastric, and great sympathetic. 



Functions. — The pharynx plays a passive part in respiration, by serving as 

 an intermediate canal between the nasal passages and the larynx. 



Its principal function, however, is connected with the digestive phenomena, 

 by its being an active agent in the first stage of deglutition — a complex and 

 rapid movement, which is executed in the following manner : The bolus of food, 

 propelled by the tongue into the pharynx, is seized by the constrictor muscles. 



Viz. 252. 



MUSCLES OF THE PHARYNGEAL AND HVOIDEAL RKGIONS. 



I, Glenoid cavity of temporal bone; 2, superior extremity of styloid b(ine; 3, tensor palati with 

 its pulley, 5; 4, stylo-pharyngeus; 6, palato-pharyngeus ; 7, circumflexus palati; 8, pterygo- 

 pharyngpus; 9, sublingual gland; 10, portion of hyoid bone; 11, hyo-pharyngeus ; 12, thyro- 

 pharyngeus ; 13, crico-pharyngeus ; 14, portion of stylo-pharyngeus; 15, hyo-thyroideus ; 16, 

 styloid bone; 17, criro-arytenoideus lateralis; 18, oesophagus; 19, sterno-maxillans and hyoideus, 

 and subscapulo-hyoideus ; 20, trachea; 21, hard palate; 22, tongue. 



which come into action successively from before to behind, in a peristaltic and 

 involuntary manner, to carry the mass to the entrance of the oesophagus. The 

 food thus passes over the opening of the larynx during pharyngeal deglutition, 

 but it cannot enter it, becauses the bolus forces back the epiglottis on this 

 aperture, which it almost exactly closes ; because, also, the passage of the food 

 prevents pulmonary inspiration, which might, if allowed to take place, divert it 

 from its natural course, and throw it into the nasal air-passages. The applica- 

 tion of the walls of the pharynx to the pellet of food during its momentary 

 passage over the larynx, prevents all communication between the external air 

 and the lungs, and only permits the elevation of the ribs with the utmost 

 difficulty. The extreme rapidity of the act of deglutition is another reason fofr 

 the food escaping the larynx. 

 31 



