THE SENSES. 271 



still doubtful). It lies like a circlet of folds before the vitreous body, around 

 the border of the lens, behind the corpus ciliare, and presents alternating 

 black and clear rays. The rays are longer than the proc. ciliares oi the cho- 

 roid, and form depressions and folds which correspond to those of the last. 

 Its posterior border is undulating and indented (ora serrata), and impinges 

 upon the anterior boundary of the Retina ; its anterior border is firmly con- 

 nected to the border of the capsule of the lens (upon the anterior surface). 

 The corona ciliaris in the foetus is supplied plentifully with blood-vessels, 

 which anastomose with those of the very vascular capsule and Choroidea; but 

 in the adult, like the hyaloid membrane, it is non- vascular. 



505. II. The organ of Hearing. Organon auditus. 



The ear, auris, consists of three parts. These are : The ex- 

 ternal, that is, the auricular cartilage and the external auditory 

 meatus. The central, that is, the tympanic cavity and the Eus- 

 tachian tube. The internal, that is, the Labyrinth. 



A. The external part. 



506. 1. The external ear, auriculus, the ear, an oval, elastic, 

 cartilaginous plate, many times curved, situated on, and firmly 

 attached by ligaments to, the lateral parietes of the head at an 

 angle of from 25 to 30, covered by the external integument. On 

 its outer surface the following parts may be observed : 



a. Concha auris, a hollow, the shape of a muscle shell, at the anterior and 

 inferior part of which the external auditory canal commences, is bounded an- 

 teriorly by 



1. Tragus, the anterior auricular valve, that is, a rounded, four-sided 

 plate, internally beset with hairs, which can close the external auditory 

 meatus in front. 



2. Antitragus, a small triangular projection at the termination of the 

 anthelix. It lies rather deeper, opposite to the tragus, and between the 

 two we find : 



incisura intertragica, a deeper and rounded excavation, above the 

 lobule of the auricle. Above and behind, the concha is bounded by : 



3. Anthelix, that is, a curvilinear elevation, which commences above 

 the antitragus, passes upwards and forwards, and terminates with two 

 crura (a sharp inferior and a blunt superior), between which is situated a 

 shallow, triangular fossa, fossa innominata. 



b. Helix, that is, the elevation which commences in the auditory concha, 

 separates it into a superior and inferior portion, then, parallel with the anthe- 

 lix, forms the external anterior reflected border of the auricle, and ceases at 

 the auricular lobule. 



Between helix and anthelix an oblong fossa, fossa navicularis s. scapha is 





