804 



DISSECTION OF THE EAR. 



inner end. 



Condition in 

 the fetus. 



attachment to the cartilage of the pinna. The inner end is smaller, 

 and is marked in the dry bone, except at the upper part where 

 there is a notch in the osseous margin, by a groove for the insertion 

 of the membrane of the tympanum ; it is so sloped that the anterior 

 wall and the floor extend inwards beyond the hinder wall and the 

 roof for nearly a quarter of an inch. 



In the foetus the osseous part of the meatus is very imperfect, 

 the floor and anterior wall being composed of fibrous tissue. After 

 birth the osseous wall is completed by an outgrowth from the ring 

 (tympanic bone) which supports the membrana tympani. 



FJQ. 295. VERTICAL SECTION OP THE MEATUS AUDITORIUS AND 

 TYMPANUM (SCARPA). 



a. Cartilaginous part of the 

 meatus. 



b. Osseous portion. 



c. Membrana tympani. 



d. Cavity of the tympanum. 



e. Eustachian tube. 



Lining Lining of the meatus. A prolongation of the integument lines 



the auditory passage, and is united more closely to the osseous than 

 to the cartilaginous portion ; it is continued over the membrane of 

 the tympanum in the form of a thin pellicle. At the entrance of 

 the meatus are a few hairs. In the subcutaneous tissue over the 



Ceniminous cartilage of the meatus lie some ceruminous glands of a yellow- 

 brown colour, resembling in form and arrangement the sweat-glands 

 of the skin ; these secrete the ear-wax, and open on the surface by 

 separate orifices ; they are absent in the osseous part, and are most 

 abundant in that small portion of the tube which is formed by 

 fibrous tissue. 



Vessels and nerves. The meatus receives its arteries from the 

 posterior auricular, the internal maxillary, and the superficial 



glands. 



Vessels. 



