248 LABORATORY MANUAL OF HUMAN ANATOMY 



responds to the third eyelid, or membrana nictitans, of lower 

 animals. The stream (rivus lacrimalis) of tears (lacrimae) run- 

 ning over the conjunctiva passes to the medial angle of the eye. 

 At the point on each lid where the eyelashes cease is a small 

 eminence, the lacrimal papilla (papilla lacrimalis). These 

 eminences are perforated, the openings looking like two minute 

 black dots (puncta lacrimalia) . The openings lead into small 

 canals, lacrimal ducts (ductus lacrimales). Pass a fine bristle 

 into each. The lacrimal apparatus will be further studied later. 



The Mouth-opening. 



Note that it is bounded by the two lips (labia on's), one supe- 

 rior (labium superius), one inferior (labium inferius). At the 

 junction of the lips at the two angles of the mouth (anguli oris) 

 are the commissures of the lips (commissurae labiorum). The 

 slit between the lips is called the rima oris. Note the curious 

 transition between skin and mucous membrane in the lip. 



Skin and Superficial Fascia. 



Observe the thinness and fineness of the skin of the face. 

 Compare its mobility with that of other parts. Which portions 

 are most firmly attached to subjacent structures? Are any 

 comedones visible! Note the distribution of the hairs of the 

 beard (barba). Observe the long, rather stiff hairs at the nose 

 openings (vibrissae). Through the skin feel the external maxil- 

 lary artery where it passes over the margin of the mandible. 

 Distend the cheeks and lips with moist cotton and stitch the 

 margins of the lips together with a fine needle. 



Make an incision through the anterior median line and re- 

 move the skin of the face, taking no fat with it. Avoid injury to 

 the upper part of the platysma, the M. risorius, and the struct- 

 ures of the eyelids. After the platysma has been carefully 

 studied, it may be removed. 



Cutaneous Muscles of Face. (Vide Fig. 104.) 



Note that the majority of the muscles of the face and scalp 

 have attachments to the skin; indeed, these muscles have been 

 derived by progressive differentiation of a primitive cervico- 

 f acial cutaneous muscle ; all of them are innervated by branches 

 of the N. f acialis, which is the nerve of the hyoid arch. Observe 

 the tendency to a grouping around various orifices, the muscles 

 acting as dilators or constrictors of these orifices. What part 

 do these muscles play in facial expression? 



