THE EXTERNAL EAR. 



1489 





Sebacf.-ous gland 



Cartilage 



of the ear. At its inner end the cartilagino-membranous meatus is attached 

 to the inferior and lateral edges of the osseous meatus, the fibrous part being 

 continuous superiorly and posteriorly with the periosteal lining of the osseous 

 canal. The osseous portion of the tube, about 14 mm. in length, is longer 

 and narrower than the cartilagino-membranous part. At its inner end it presents 

 a narrow groove, the sulcus tympanicus, for the insertion of the tympanic 

 membrane. The sulcus extends around the sides and ffoor of the canal, but is 

 deficient above. 



The skin lining the external auditory canal is closely attached to the underlyino- 

 cartilaginous portion of the tube. The skin measures about 1.5 mm. in thick- 

 ness, but is much thinner within the bony canal, except along the roof, where it 

 remains relatively thick. Over the outer surface of the tympanic membrane the 

 skin is reduced to 



a very delicate and ^'"^- ^^49- 



smooth investment, 

 covered by a corre- 

 spondingly attenu- 

 ated epidermis, and 

 a suggestion of sub- 

 cutaneous tissue. 

 Numerous fine hairs 

 and large sebace- 

 ous glands occur 

 in the cartilaginous 

 portion, but dimin- 

 ish in size and fre- 

 quency towards the 

 bony canal, in which 

 they are entirely 

 wanting. Within the 

 cartilaginous meatus 

 and along the roof 

 of the bony tube, the 

 skin is closely be- 

 set with the large 

 coiled ceruminous 

 glands, which re- 

 semble in structure 

 modified sweat 

 glands. Like the 

 latter, the cerumin- 

 ous glands consist of 

 a deeper and wider 

 coiled portion, the 



secretory segment, and a long narrow excretory duct, which ends in most cases inde- 

 pendently on the free surface of the skin, but sometimes, particularly in the very 

 young child, it opens into the duct of a sebaceous gland. The cuboidal secreting 

 cells contain yellowish brown pigment particles and granules resembling fat. The 

 ear-wax or cerumen is, as usually found, the more or less dried mixture of the 

 secretions derived from both varieties of glands, together with discarded squamous 

 epidermal cells. 



Vessels. — The arteries distributed to the external auditory canal are from three 

 sources: (a) anterior branches of the superficial temporal supply the external por- 

 tion of the meatus ; (<5) the deep auricular artery, a branch of the internal maxillary, 

 passes to the deeper portions ; whilst (<:) the posterior auricular provides branches 

 for the posterior and superior surfaces. The arteries destined for the interior of the 

 canal pierce the membranous roof of the cartilaginous meatus, the fissures of Santo- 

 rini and the fibrous tissue connecting the cartilaginous with the bony portion of the 

 tube. They form capillary net-works within the perichondrium and periosteum and, 



94 



Ceruminous 

 glaiul 



Conum 



Hair-follicle 



Transverse section of skin lining cartilaginous portion of external 

 auditory canal. X 30. 



