830 THE ORGANS OF SENSE. 



(&) On the medial surface (Fig. 706) 



1. M. transversus auriculae consists of scattered fibres, which stretch from the 

 eminentia conchae to the convexity of the helix. 2. M. obliquus auriculae (Tod) 

 comprises a few fasciculi, which run obliquely or vertically across the furrow corre- 

 sponding with the crus antihelicis inferior. A small muscle, the m. stylo-auricu- 

 laris, sometimes extends from the root of the styloid process to the cartilage of 

 the meatus. 



Skin of the Auricula. The skin covering the auricle is thin and smooth, 

 and is prolonged, in the form of a tube, as a lining to the external acoustic 

 meatus. On the lateral surface of the auricula, it adheres firmly to the subjacent 

 perichondrium. Strong hairs are present on the tragus and antitragus, and also 

 in the incisura intertragica, forming the barbula hirci, which guard the entrance to 

 the concha ; soft downy hairs are found over the greater part of the auricula and 

 point towards the tuberculum auriculae. Sebaceous glands, present on both 

 surfaces of the auricle, are most numerous in the concha and fossa triangularis. 

 Sudoriferous glands are found on the medial surface ; few or none on the lateral 

 surface. 



Vessels of the Auricula. The arteries of the auricle are derived (a) from tlie superficial 

 temporal, which sends two or three branches to the lateral surface ; and (6) from the posterior 

 auricular, which gives three or four branches to the medial surface. From the posterior auricular 

 artery two sets of twigs are prolonged to the lateral surface, one turning round the free margin 

 of the helix, and the other passing through small fissures in the cartilage. The veins from the 

 lateral surface open into the superficial temporal vein ; those from the medial surface chiefly join 

 the posterior auricular vein, but some communicate with the mastoid emissary vein. The 

 lymph vessels take three directions, viz. : (a) forwards to the parotid lymph glands, and 

 especially to the anterior auricular gland in front of the tragus ; (6) downwards to the lymph 

 glands which accompany the external jugular vein, and to the lymph glands under the sterno- 

 cleidomastoideus ; and (c) backwards to the posterior auricular lymph glands. 



Nerves of the Auricula. The muscles of the auricle are supplied by the facial nerve. 

 The skin receives its sensory nerves from (a) the great auricular, which supplies nearly the 

 whole of the medial surface, and sends filaments in company with the branches of the posterior 

 auricular artery to the lateral surface ; (b) the auriculo-temporal, which supplies the tragus and 

 ascending part of the helix ; (c) the lesser occipital, which sends a branch to the upper part of the 

 medial surface. 



MEATUS ACUSTICUS EXTERNUS. 



The external acoustic meatus (Figs. 707, 708) is the passage leading from 

 the concha to the membrana tympani. Its average length, measured from 

 the bottom of the concha, is about 24 mm., but, if measured from the level 

 of the tragus, about 35 mm. On account of the obliquity of the membrana 

 tympani the anterior and inferior walls of the meatus are longer than the posterior 

 and superior. The meatus consists of two parts, viz. : (a) an external portion, 

 the pars cartilaginea, about 8 mm. in length ; and (6) an internal portion, the pars 

 ossea, about 16 mm. in length. The entire meatus forms a somewhat S -shaped 

 bend (Fig. 708), and may be divided into three portions external, intermediate, 

 and internal ; each is directed medialwards, but, in addition, the external part is 

 inclined forwards and slightly upwards; the intermediate, backwards; and the 

 internal, the longest, forwards and slightly downwards. On transverse section the 

 canal is seen to be elliptical, its greatest diameter having an inclination downwards 

 and backwards. Widest at its lateral extremity, it becomes somewhat narrower 

 at the medial end of the pars cartilaginea; once more expanding in the lateral 

 portion of the pars ossea, it is again constricted near the medial end of the 

 latter, where its narrowest part, or isthmus, is found at a distance of about 19 mm. 

 from the bottom of the concha. The medial extremity of the meatus is nearly 

 circular and is closed by the membrana tympani. 



Bezold gives the diameters of the meatus as follows : 



Greatest. Least. 



At the commencement of the pars cartilaginea . . 9 '08 mm. 6 '54 mm. 



At the end 7 '79 mm. 5-99 mm. 



At the commencement of the pars ossea . . . 8'67 mm. 6'07 mm. 



At the end 8-13 mm. 4-60 mm. 



