24 U.S. NATIONAI. MUSEUM BULLETIN 2 73 



join the rest of the muscle after receiving the bundles of the styloglos- 

 sus when this is present. Some of the Ungual elements arise from the 

 sides of the hyoglossal membrane adjacent to those of the middle 

 constrictor (fig. 8). The fibers of the superior constrictor previously 

 described as coming from the lateral air sacs (Schon, 1964) are now 

 regarded as belonging to the middle constrictor. 



Nerve supply: Branches of the pharyngeal plexus. 



Function: Constrictor of the upper pharynx and retractor of the 

 tongue when complete. 



M. constrictor pharyngis medius: It is the smallest of all three 

 pharyngeal constrictors and can be well visuaUzed only after ablation 

 of both cornu branchiale I (see Starck and Schneider, 1960, for defi- 

 nition of this term) and the thyroid lamina. Its fibers of origin are 

 arranged into three groups. (1) Pars lingualis originates from the 

 hyoglossal membrane and intrinsic lingual muscles by a mixture of 

 fleshy and fibrous fascicles which are immersed in abundant adipose 

 tissue (fig. 8). They run backward around the root of the tongue to 

 join the rest of the muscle. (2) The greater number of fibers arise 

 Avithin a fatty environment from the membrane of the laryngeal 

 saccules and form the pars membranacea (fig. 8). They are initially 

 covered by the thyroid lamina but further dorsally are found above 

 its cranial border and lined by the thin thyrohyoid membrane. 

 These fascicles cross the epiglottis in a craniodorsal direction and 

 join those of the rest of the muscle under the bicornual articulation. 

 (3) Pars cornuaUs is represented by a small number of fibers which, 

 arising at the distal end and medial surface of cornu branchiale I, 

 contribute immediately to the formation of the muscle. All fibers of 

 the middle constrictor run dorsally with a slight cranial inclination 

 to end on the midhne raphe of the back of the pharynx. 



Nerve supply : Branches from the pharyngeal plexus. 



Function: Besides its role as a pharyngeal sphincter by the con- 

 traction of all its fibers, the muscle can also act in emptying the 

 laryngeal saccules through its pars membranacea. The constrictor 

 effect upon the alimentary canal probably takes place in swallowing 

 simultaneously with the contraction of the levators of the larynx. 

 At this moment the palatopharyngeus and the middle constrictor 

 will contribute to isloate the rhino- from the oro- and laryngopharynx 

 by pressing the walls of the pharynx against the prominent epiglottis. 



M. constrictor pharyngis inferior: Four parts can be described in 

 this large muscle according to the different cartilaginous areas from 

 which it arises (fig. 8). (1) Pars thyropharyngea: A great many 

 fleshy fibers come from the lateral surface of the thyroid lamina where 

 they are covered by the costothyroideus and thyrohyoideus. This 

 origin extends from the upper to near the lower margin of the lamina. 



