838 THE OKGANS OF SENSE. 



in the cartilage; sometimes it is completely separated into several pieces, or 

 accessory islands may be observed in the roof, floor, or membranous lamina. 



The upper and medial surfaces of the medial lamina are firmly fixed to the base 

 of the skull, where it lies in a groove, the sulcus tubae auditivae, between the great 

 wing of the sphenoid and the petrous part of the temporal. Extending forwards 

 on to the root of the pterygoid process this sulcus ends at a projection, the proeessus 

 tubarius, on the medial pterygoid lamina. The tensor veli palatini muscle lies on 

 the lateral side of the tube and receives some fibres of origin from its lamina 

 lateralis; these fibres constitute the dilatator tubas muscle (Elidinger). On the 

 medial side of the cartilage are the levator veli palatini and the mucous membrane 

 of the pharynx. The membranous lamina consists of a strong fibrous membrane, 

 stretching between the two edges of the cartilage, and so completing the lower and 

 lateral walls of the tube. Thin above, it becomes thickened below and forms the 

 fascia salpingopharyngea of Troltsch, which gives origin to some of the fibres of the 

 tensor veli palatini muscle. Between this fascia and the mucous lining of the tube 

 is a layer of adipose tissue. 



The pharyngeal orifice of the auditory tube, triangular or oval in shape, is situated 

 on the lateral wall of the nasal part of the pharynx, the centre of the opening 

 being on a level with the posterior end of the inferior nasal concha. It is 

 bounded above and behind by a pad, the torus tubarius, produced by the base of 

 the cartilage, which there abuts against the mucous membrane ; the posterior part 

 of the torus is very prominent and forms the anterior boundary of the pharyngeal 

 recess. Prolonged downwards from it is an elevation of the mucous membrane, 

 termed the plica salpingopharyngea, which covers the small salpingopharyngeus 

 muscle. From the upper part of the torus an indistinct fold, the plica salpingo- 

 palatina, extends to the palate. 



The mucous lining of the tube is continuous behind with that of the tympanic 

 cavity, and in front with that of the nasal part of the pharynx. It is thin in the 

 pars 03sea, contains few, if any, mucous glands, and is firmly fixed to the bony wall ; 

 in the pars cartilaginea it is loose and thrown into longitudinal folds. Numerous 

 mucous glands open into the tube near its pharyngeal orifice, and here also exists 

 a considerable amount of adenoid tissue, which constitutes the " tube-tonsil " of 

 Gerlach. This adenoid tissue is continuous with that of the nasal part of the 

 pharynx, and, like it, is especially well developed in children. The lumen of the 

 tube is lined with ciliated columnar epithelium. 



The tube is opened, during deglutition, by the dilatator tubse and salpingo- 

 pharyngeus muscles. The former springs superiorly from the cartilaginous hook of 

 the tube, and blends inferiorly with the tensor veli palatini. When the dilatator 

 tubse contracts, the cartilaginous hook and the membranous lamina of the tube are 

 drawn lateralwards and forwards. Some anatomists believe that the entire tensor veli 

 palatini acts chiefly as a dilator of the tube, and Kiidinger named it the abductor 

 tubse. The salpingopharyngeus muscle draws downwards and backwards the 

 medial lamina, increasing the angle between it and the lateral lamina. Some 

 difference of opinion exists as to the precise action of the levator veli palatiiii; 

 probably it assists in opening the tube. 



The auditory tube receives its blood-supply from the ascending pharyngeal artery, and from 

 the middle meningeal artery and the artery of the pterygoid canal, both of which are branches 

 of the internal maxillary artery. Its veins form a network which drains into the pterygoid 

 venous plexus. The sensory nerves of the tube are derived from the tympanic plexus and from 

 the pharyngeal branch of the spheiio-palatine ganglion. 



The auditory tube of the child differs considerably from that of the adult; its lumen is 

 relatively wider, its direction more horizontal, and its pars ossea relatively shorter. Kunkel 

 states that its pharyngeal orifice is below the level of the hard palate in the foetus ; at birth 

 it is on the same level as the palate, whilst at the fourth year it is 3 to 4 mm., and in the adult 

 10 mm., above it. In the child the pharyngeal orifice forms a narrow fissure, and its cartilage 

 projects less towards the middle line. 



OSSICULA AUDITUS. 



The auditory ossicles form an articulated column connecting the lateral 

 with the medial wall of the tympanic cavity; they are named, from without 



