MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 25 



There is no trace of a linea obliqua or superior and inferior tubercles. 

 The laminar fascicles are all horizontally directed toward the dorsal 

 midline raphe where they are inserted. (2) Pars cricopharyngea: 

 The distal border of the cricoid arch gives rise to several bundles which, 

 running more or less horizontally backward, reach the level of the 

 cricothyroid articulation. They now change their direction and pass 

 cranially covering the lower horn up to the level of the lower laminar 

 margin. A new change in direction takes place whereby the fascicles 

 join those of the pars thyropharyngea mth which they end on the 

 dorsal midline raphe of the pharynx. (3) Pars tracheopharyngea: 

 Fleshy fibers originate from the tip of the first tracheal cartilage and 

 form a muscular band which runs backward along the tracheocricoid 

 junction. It turns cranially around the end of the lower thyroid horn 

 and ascending parallel to the posterior border of the cartillage reaches 

 the level of the lower margin of the lamina. The fascicles now pass 

 horizontally toward the midline raphe, forming a single muscular 

 sheet with those of parts (1) and (2). (4) Pars cornuopharyngea: A 

 small group of fibers arises on the posterior border of the cornu 

 inferius under cover of the ascending portions of the tracheal and 

 cricoid parts which it joins. The cricopharyngeal sphincter is there- 

 fore formed by fascicles which from each side of the respiratory canal 

 are first directed dorsally, then ascend to change again their direction 

 and pass dorsomedially toward the back of the pharynx. 



Nerve supply: The ramus externus of the n. laryngeus superior is 

 the main contributor to the formation of the pharyngeal plexus which 

 sends several branches to this muscle. 



Function: Fibers of pars thyropharyngea are sphincteric to the 

 laryngopharynx. Their constrictor effect over this part of the 

 digestive tube is extended to the laryngeal saccules found between the 

 inner surface of the thyroid lamina and the vestibule of the larynx. 

 Air will be squeezed out of these sacs on contractions of the muscle. 

 By the same mechanism the deep piriform recesses of the pharynx 

 will also be reduced. An interesting function could possibly be ascribed 

 to the cricopharyngeal sphincter on the basis of the direction followed 

 by its fibers. Its contraction could tilt the cricoid cartilage bringing 

 the arch downward and therefore the arytenoids forward. The 

 cornual fibers and the bending of both pars trachealis and cricoidea 

 around the tip of the lower horn ensures that the puUing effect is 

 properly carried. This action should have influence in the production 

 of certain tones as the displacement forward of the arytenoids brings 

 their vocal process closer to the thyroid angle vnih the consequent 

 relaxation of the vocal folds. 



M. palatopharyngeus: It is well developed and contributes in the 

 formation of the lateral and posterior waUs of the pharynx. Origin 



