422 SENSE-ORGANS AND INTEGUMENT. 



These two bundles are distinct except at their origin, and 

 are sometimes considered as separate muscles. 



Relations. Outer surface with the tragicus lateralis (4) and 

 the fat about the concha. Inner surface with the concha. 

 Action. Flexes the concha. 



Strauss-Durckheim describes under the name cornetocon- 

 chaeus a small muscle bridging the deep groove caused by the 

 folding of the medial surface of the concha, its proximal end 

 being close to the insertion of the abductor auris brevis (page 

 100). This muscle was absent in all of the cases examined for 

 its presence. 



M. conchaeus externus (Fig. 169, 9). A quadrilateral 

 muscle on the lateral surface of the concha. The cranial end 

 of this muscle is attached to the concha a short distance distad 

 of the antitragus along a dorsoventral line six to eight milli- 

 meters in length ; the fibres pass thence caudodorsad a distance 

 of about one centimeter, where they are again attached to the 

 concha. The muscle thus bridges a shallow depression on the 



lateral surface of the concha. 



Action. Constricts the concha. 

 The Middle Ear. 

 The middle ear is enclosed in a 

 cavity within the tympanic bulla. 

 Its outer boundary, as well as the 

 inner boundary of the external ear, 

 FIG. 170. TYMPANIC MEMBRANE, is formed by the tympanic mem- 



VlEWED FROM THE INNER SlDE. brane pj j ^ Th j s fc 



The outer wall of the bulla has ., , , , 



been removed, carrying with it the semitransparent membrane attached 



tympanic membrane with the mal- to the bony ring (a) Surrounding the 

 leus and incus; these are now . , 11- 



viewed from the side that was inner end of the external auditory 



turned toward the cavity , bony mea tus. It is OVal in outline. Across 

 ring forming inner end of external 



auditory meatus; b, b' , malleus; c, the dorsal third of its inner surface 

 tympanic membrane; d incus; e, rung th handle of the ma ll e us (b\ 

 lenticular process; /, chorda tym- 



pani nerve; g, cartilaginous sup- to which the membrane is firmly 

 port for chorda tympani nerve. attached and which by pulling on 



the membrane gives it the form of a cone instead of a flat sur- 

 face. The apex of the cone is directed mediad. 



The middle ear, or cavum tympani, is an ellipsoidal cavity 



