DISSECTION OF THE HEAD AND NECK 251 



(ha) Buccopharyngeal fascia (fascia buccopharyngea) . 



In cleaning this muscle avoid injury to the motor 

 branch from the N. facialis and the sensory buc- 

 cinator nerve from the N. trigeminus. 

 Constrictors of mouth. 



(a) Orbicular muscle of mouth (M. orbicularis oris). 



As a muscle of vegetable life it closes the mouth to hinder 

 exit of saliva and food, prevents entrance of foreign bodies, 

 is prehensile in taking food and liquid, and is active in suction 

 and mastication; as a muscle of relational life it closes lips 

 partly or completely in physical effort, in articulation of words, 

 whistling, playing musical instruments, kissing, etc. 



Note the division into a pars externa and a pars interna. 

 The latter is unaffected in cerebral hemiplegia, and the patient 

 can still close the mouth, whistle, and speak. Both are affected 

 in glosso-labio-laryngeal paralysis, and the patient can no 

 longer whistle, retain saliva, or pronounce the letters o and u. 



(b) Compressor muscle of lips (M. compressor labiorum [Kleinii]) 



(0. T. rectus labii of Aeby). 



(c) Incisive muscle of upper lip (M. incisivus labii superioris). 



(d) Incisive muscle of lower lip (M. incisivus labii inferioris). 



The incisive muscles act along with the M. orbicularis oris in 

 pointing the mouth : they are sometimes called the " muscles 

 of pouting." 

 Eeferences. 



1. On the origin of the facial muscles : 



Gegenbaur, C., Lehrbuch der Anatomic des Menschen. 

 Ruge, Untersuchungen iiber die Gesichtsmuskulatur der Primaten, 

 Leipzig, 1887. 



2. On the muscles as agents of expression : 



Bell, C., Anatomy and Physiology of Expression, 1844. 

 Duchenne (of Boulogne), Mecanisme de la physionomie humaine, 



1852. 

 Darwin, C., Expression of Emotions in Man and Animals. 



Region of Parotid Gland. 



In the study of the deep cervical fascia the parotideomasse- 

 teric fascia (fascia parotideomasseterica) has been observed 

 passing upward to become attached to the zygoma. On its sur- 

 face the ramus anterior of the N. auricularis magnus was noted. 

 The fascia is to be very carefully removed and the parotid gland 

 defined. 



Observe the exact position and relations of the parotid gland 

 (glandula parotis). Find its excretory duct (ductus parotideus 

 [Stenonis] ) and follow it throughout its course. Cut into it and 

 pass a probe through into the mouth. Note the position of the 

 oral termination of the duct. In relation to the upper border of 

 the duct, note the accessory parotid gland (Gl. parotis accesso- 



