188 



MUSCLES OF THE HEAD AND NECK. 



The inferior constrictor arises from the side of the cricoid cartilage, and 

 from the oblique lateral ridge and upper and lower borders of the thyroid 

 cartilage, and curves backwards, expanding as it proceeds, and unites with 

 its fellow in the middle line behind the pharynx. The direction of the 

 inferior fibres is horizontal, concealing and overlapping the commencement 

 of the oesophagus ; the rest ascend with increasing degrees of obliquity, and 

 cover the lower part of the middle constrictor. 



The outer surface of the muscle is in contact at the side of the larynx with the 

 thyroid body, the carotid artery, and the sterno-thyroid muscle ; and from this last, 

 where the two muscles meet on the thyroid cartilage, some fibres are continued into the 

 constrictor. The two laryngeal nerves pass inwards to the larynx, close respectively 

 to the upper and lower margins of this constrictor the upper being interposed between 

 it and the middle constrictor, the lower between it and the oesophagus. 



The inferior constrictor was described by the older anatomists as two muscles which 

 received various names, the most appropriate of these being thyro-pharyngeus and 

 crico-pharyngeus. In some animals they are found quite distinct from one another. 



F5g 164. Fig. 164. VIEW OP 



THE MUSCLES OF 

 THE PHARYNX, &o. 

 FROM BEHIND (after 

 Bourgery.) 



The back part of 

 the skull, the ver- 

 tebral column and 

 back parts of the 

 ribs are removed, a, 

 cut surface of the 

 basilar process ; &, 

 the clavicle ; c, the 

 first rib ; d, the 

 ramus of the lower 

 jaw ; e, posterior ex- 

 tremity of the great 

 cornu of the byoid 

 bone ; /, posterior 

 surface of the manu- 

 brium of the ster- 

 num ; 1, superior 

 constrictor muscle of 

 the pharynx ; above 

 it, the fibrous mem- 

 brane which closes 

 the pharynx; 2, mid- 

 dle constrictor ; 2', 

 a dotted line, indi- 

 cating the direction 

 of the lower part of 

 the muscle ; 3, the 

 inferior constrictor ; 

 4, oesophagus ; 5, in- 

 ternal pterygoid ; 6, 

 stylo-glossus ; 7, pos- 

 terior belly of the 



digastric ; 8, a portion of the stylo-hyoid surrounding the tendon of the digastric ; 9, 

 sterno-mastoid ; 10, upper belly of the omo-hyoid ; 11, sterno-thyroid muscle. 



The middle constrictor arises from the upper part of the great cornu of 

 the os hyoides, from the smaller cornu, and from the stylo-hyoid ligament : 

 its fibres, diverging greatly, pass back to the middle line of the pharynx behind, 



