THE MEMBRANA TYMPANI. 215 



Light-spot, a triangular reflection, its apex at the tip of 



the malleus-handle, its base extending to the periphery 



of the membrane. It is due to the concavity of the 



drumhead. 



Umbo, or shadow, is the darker central portion. 

 ShrapnelPs Membrane, is the upper posterior part of 



the drumhead, where it is somewhat flaccid. 

 Rivinian Foramen, a minute opening supposed to exist 



in the portion called Shrapnell's membrane. 



In what direction is the Membrana Tympani placed ? Obliquely 

 inwards and forwards, almost forming a continuation of the posterior wall of 

 the external auditory canal. 



Describe the Structure of the Membrana Tympani. It is composed 

 of 3 layers, as follows : 



External, or Dermoid Layer, continuous with the integument lining the 



external auditory canal. 

 Middle Layer, or Lamina Propria, formed of outer radiating fibres, and 



inner circular ones. Between these two sets of fibres are situated the 



short process and handle of the malleus. 

 Internal or Mucous Layer, is continuous with the mucous lining of the 



tympanum. 

 Tendinous Ring (At, Fig. 106), surrounds the margin of the membrane, 



being received into the sulcus tympanicus. Its anterior and posterior ends 



are shown by v and h in Fig. 106. 



What Structures are presented by its Internal Surface ? A fibrous 

 fold descends from the upper portion of the marginal ring, for a short distance 

 along the malleus-handle, forming the 

 Anterior and Posterior Pouches, one on each side of the malleus-handle, 



opening downwards. 

 Tendinous Bands, 4 or 5, converge from the posterior margin to the 



middle of the malleus-handle. 



What Arteries Supply the Membrana Tympani ? The 



Deep Auricutar,brsinch of the internal maxillary, supplies the external layer. 



and forms with the Tympanic Branches a capillary plexus in the middle 



layer, (von Trolsch, Roosa, etc.) 

 Tympanic, branches of the internal maxillary and internal carotid arteries, 



supply the internal layer, and anastomose on the membrana tympani with 



the 

 Vidian and Stylo-mastoid, branches respectively of the internal maxillary 



and posterior auricular branches of the external carotid. 



