456 ORGAN OF HEARING. 



muscle, which arises from the same ridge, and in its action upon the 

 lachrymal canals may serve to compress the lachrymal sac. 



The Nasal duct is a short canal about three-quarters of an inch in 

 length, directed downwards, backwards, and a little outwards to the infe- 

 rior meatus of the nose, where it terminates by an expanded orifice. It 

 is lined by mucous membrane, which is continuous with the conjunctiva 

 above, and with the pituitary membrane of the nose below. Obstruction, 

 from inflammation and suppuration of this duct, constitutes the disease 

 called fistula lachry mails. 



Vessels and Nerves. The lachrymal gland is supplied with blood by 

 the lachrymal branch of the ophthalmic artery, and W 7 ith nerves by the 

 lachrymal branch of the ophthalmic and orbital branch of the superior 

 maxillary. 



THE ORGAN OF HEARING. 



The apparatus of hearing is composed of three parts ; the external ear, 

 middle ear or tympanum, and internal ear or labyrinth. 



The EXTERNAL EAR consists of two portions, the pinna and meatus ; the 

 former representing a kind of funnel which collects the vibrations of the 

 atmosphere, producing sounds, and the latter a tube which conveys the 

 vibrations to the tympanum. 



The PINNA presents a number of holes and hollows upon its surface, 

 which have different names assigned to them. Thus, the external folded 

 margin is called the helix (sXjf, a fold). The elevation parallel to and in 

 front of the helix is called antihelix (dv<n, opposite). The pointed process, 

 projecting like a valve over the opening of the ear from the face, is called 

 the tragus (r^ayog, a goat), probably from being sometimes covered with 

 bristly hair like that of a goat ; and a tubercle opposite to this is the anti- 

 tragus. The lower dependent and fleshy portion of the pinna is the- 

 lobulus. The space between the helix and antihelix is named the fossa 

 innominata. Another depression is observed at the upper extremity of 

 the antihelix, which bifurcates and leaves a triangular space between its 

 branches, called the scaphoid fossa ; and the large central space, to which 

 all the channels converge, is the concha, which opens directly into the 

 meatus. 



The pinna is composed of integument, fibro-cartilage, ligaments, and 

 muscles. 



The Integument is thin, contains an abundance of sebiparous glands, 

 and is closely connected with the fibro-cartilage. 



The Fibro-cartilage gives form to the pinna, and is folded so as to pro- 

 duce the various convexities and grooves which have been described upon 

 its surface. The helix commences in the concha, and partially divides 

 that cavity into two parts; on its anterior border is a tubercle for the 

 attachment of the attrahens aurem muscle, and a little above this a small 

 vertical fissure, the fissure of the helix. The termination of the helix and 

 antihelix forms a lengthened process, the processus caudatus, which is 

 separated from the concha by an extensive fissure. Upon the anterior 

 surface of the tragus is another fissure, the fissure of the tragus, and in 

 the lobulus the fibro-cartilage is wholly deficient. The fibro-cartilage of 

 the meatus, at the upper and anterior part of the cylinder, is divided from 



