92 bulletin: museum of comparative zoology. 



S. SUMMARY ON THE DISTRIBUTION OF NERVES IX, 

 X AND XI I. 



These nerves contain viscero-sensory (red), viscero-motor (dark 

 blue), and somatic motor (pale blue) elements. The viscero-sensory 

 (red) are contained in IX and X, and reach their end organs by two 

 nerves, (a) the pharyngo-laryngeal branch, coming off from XII, 

 and (b) the visceral and recurrent rami of X. The sensory elements 

 of the former appear to be distributed to the mucous membrane of 

 the pharynx lateral and anterior to the glottis; those of the latter (not 

 including those in the posterior visceral ramus) to the pharynx wall 

 posterior to (a) and, through the ramus recurrens X, to the tracheal 

 and laryngeal epithelium itself. 



The viscero-motor elements (dark blue) are carried in the pharyngo- 

 laryngeal ramus of XII (excepting the fine motor fibers to the m. con- 

 strictor jugulae) and may reasonably be assumed to be the same as 

 those found in the coarse fibered roots of IX and X. They first give 

 off fibers to the cerato-hyoideus muscle, then, after losing the sensory 

 elements to the pharyngeal wall, they form a partial crossing and each 

 has a bilateral distribution to the laryngeal muscles. 



The somatic motor components (pale blue) comprise the three roots 

 of XII. These differ from the somatic motor of the spinal nerves in 

 presenting collectively a much smaller-fibered nerve. A marked 

 exception exists however, in the third root, which possesses a cervical 

 part and a hypoglossal part, the two standing in contrast to each other 

 in size of fibers. The cervical part is distributed to the dorso-lateral 

 longitudinal neck muscle. The hypoglossal part, combining with all 

 the components of the other two roots to form the main trunk of XII, 

 innervates all the muscles of the ventral longitudinal series except 

 those extending from the girdle to the hyoid apparatus and the 

 cerato-hyoideus. 



T. ADDITIONAL INNERVATION TO THE VENTRAL 

 HEAD REGION. 



The other muscles of the ventral head region are supplied by V and 

 VII, thus indicating their visceral origin. Nerve VII innervates the 

 digastric and superficial constrictors, i. c, sphincter colli and mylo- 

 hyoideus in part; V innervates the mandibular series and all but the 



