914 THE ORGANS OF SENSE. 



The Musculus helicis major is a narrow vertical band of muscular fibres, situated 

 upon the anterior margin of the helix. It arises below from the process of the 

 helix, and is inserted into the anterior border of the helix, just where it is about 

 to curve backward. It is pretty constant in its existence. 



The Musculus helicis minor is an oblique fasciculus, attached to that part of 

 the helix which commences from the bottom of the concha. 



The Tragicus is a short, flattened band of muscular fibres situated upon the 

 outer surface of the tragus, the direction of its fibres being vertical. 



The Antitragicus arises from the outer part of the antitragus : its fibres are 

 inserted into the processus caudatus of the helix. This muscle is usually very 

 distinct. 



The Transversus auricula? is placed on the cranial surface of the pinna. It 

 consists of radiating fibres, partly tendinous and partly muscular, extending from 

 the convexity of the concha to the prominence corresponding with the groove of 

 the helix. 



The Obliquus auris (Todd) consists of a few fibres extending from the upper 

 and back part of the concha to the convexity immediately above it. 



The arteries of the pinna are the posterior auricular from the external carotid, 

 the anterior auricular from the temporal, and an auricular branch from the 

 occipital artery. 



The veins accompany the corresponding arteries. 



The nerves are the auricularis magnus, from the cervical plexus ; the posterior 

 auricular, from the facial to the muscles of the pinna ; the auricular branch of 

 the pneumogastric ; the auriculo-temporal branch of the inferior maxillary nerve ; 

 the occipitalis minor from the cervical plexus ; and the occipitalis major or internal 

 branch of the posterior division of the second cervical nerve. 



The Auditory Canal (meatus auditorius externus} extends from the bottom 

 of the concha to the membrana tympani. It is about an inch and a quarter 

 in length ; its direction is obliquely forward, inward, and downward. At first it 

 slightly ascends, while in the middle portion it makes a sharp bend backward. It 

 forms an oval cylindrical canal, the greatest diameter being in the vertical direction 

 at the external orifice, but in the transverse direction at the tympanic end. The 

 calibre of the canal is narrowest about the middle. The membrana tympani, which 

 occupies the termination of the meatus, is obliquely directed, in consequence of 

 which the floor of the canal is longer than the roof, and the anterior wall longer 

 than the posterior. The auditory canal is formed partly by cartilage and mem- 

 brane, and partly by bone, and is covered by skin. 



The cartilaginous portion is about half an inch in length, being rather less than 

 half the canal ; it is formed by the cartilage of the concha and tragus, prolonged 

 inward, and firmly attached to the circumference of the auditory process of the 

 temporal bone. The cartilage is deficient at its upper and back part, its place 

 being supplied by fibrous membrane. This part of the canal is rendered extremely 

 movable by two or three deep fissures (incisurce Santorini], which extend through 

 the cartilage in a vertical direction. 



The osseous portion is about three-quarters of an inch in length, and narrower 

 than the cartilaginous portion. Its inner end is marked, except at its upper part, 

 by a narrow groove (sulcus tympanicus] for the insertion of the membrana tym- 

 pani. The bony ridge, external to the sulcus, is the remnant of the foetal tym- 

 panic ring. It also is deficient above, and this deficiency is known as the notch 

 of Eivinus. The ends of the incomplete ring bound the notch, and are known 

 as the anterior and posterior tympanic spines. Its outer end is dilated, and rough, 

 in the greater part of its circumference, for the attachment of the cartilage of the 

 pinna. Its vertical transverse section is oval, the greatest diameter being from 

 above downward. The front and lower parts of this canal are formed by a curved 

 plate (tympanic plate) of bone, which, in the foetus, exists as a separate ring 

 (tympanic ring) incomplete at its upper part. 



The skin lining the meatus is very thin, adheres closely to the cartilaginous 



