I502 



HUMAN ANATOMY. 



belongs to the bony division, whilst the remainder is contributed by the cartilaginous 

 division of the tube. With the sagittal plane it forms an angle of 45°, and with the 

 horizontal plane one of about 33°. With the long axis of the external auditory 

 canal it forms an angle of from i35°-i45°, opening outward. The cartilaginous and 

 bony divisions of the tube do not lie exactly in the same plane, but join at a very 

 obtuse angle opening outward. The tube has somewhat the shape of an hour glass, 

 being wider at the ends and narrowed at the junction of the cartilaginous and bony 

 portions into the isthmus, where its height is about 3 mm. and its breadth about half 

 as much. 



The osseous or tympanic portion (pars ossea) about 12 mm. long, is bounded 

 above by the tegmen tympani and the canal for the tensor tympani muscle, from 

 which it is incompletely separated by the processus cochleariformis. Below and 

 internal to it lies the canal for the carotid artery. Its lumen is irregularly triangular 

 in cross-section. 



Fig. 1261. 



Tympanic membrane 

 Tympanic cavity 

 Antrum 

 Condyle of jaw 



Basilar process 



External audi- 

 tory canal 



Parotid gland 



Fossa of Rosen- 



muller 



Cartilage of. 



Eustachian tube 



Eustacliian tube 



Levator palati 

 Tensor palati 



Hamular process' 



Palatal raphe 



Palatal rugse^ 



Internal auditor^' canal 



Right internal carotid artery 



Incisor canal 



Tympanic membrane 



External auditory 

 meatus 



Parotid gland 



External 

 pterj'goid muscle 



Ramus of jaw 

 Internal pterygoid 

 muscle 

 Soft palate 



Masseter muscle 



.Vestibule 



Buccinator muscle 



Incisive pad 



Anterior part of section through head at plane shown in small outline figure, viewed from below; left 

 Eustachian tube exposed throughout its length. Drawn from preparation made by Professor Dwight. 



The cartilaginous or pharyngeal portion (pars cartilaginea) is about 25 

 mm. (i in.) in length and attached to the rough oblique margin of the anterior 

 end of the osseous portion of the tube. 



Its posterior wall is formed by a plate of cartilage fcartilago tubae auditivae), the 

 upper margin of which is curled outward upon itself to form a gutter, which appears 

 on transverse section as a hook, whose inner and outer plates are known as the 

 mesial and lateral lamina respectively. The interval between the margins of this 

 cartilaginous groove presents outward and forward and is filled up with a strong 

 fibrous membrane, thus completing the canal. Therefore part of the anterior wall 

 and the posterior superior wall of the tube are formed by this cartilage and the rest 

 of the anterior wall and all of the inferior by fibrous tissue. The cartilage is attached 

 to the base of the skull and frequently is deficient in places, sometimes being 

 divided into several pieces. At birth the cartilage is entirely of the hyaline variety, 

 but later this is more or less extensively replaced, particulary in the pharyngeal 

 division, by fibrocartilage, except in the upper part where the hyaline cartilage 



