174 DISSECTION OF THE DOG 



gives attachment to some of their fibres. It is continuous with the periosteum 

 covering the bones of the base of the skull and with the other connections of 

 the pharynx. 



The mucous membrane of the pharynx is moderately thick and contains 

 collections of lymphoid tissue. In the dorsal part of the tube it is redder in 

 colour and somewhat softer than in the more ventral and caudal portion. 

 The junction of the pharynx with the oesophagus is well defined by a 

 transverse mucous fold. 



The cavity of the pharynx (cavum pharyngis) is divisible into dorsal and 

 ventral portions. The dorsal part communicates with the nasal cavities by 

 the posterior nares, and is co-extensive with the soft palate. It is respiratory 

 only. The ventral part of the cavity is both respiratory and alimentary in 

 function, inasmuch as it communicates with the mouth and nose in the one 

 direction, and with the oesophagus and larynx in the other. 



In the cavity seven openings must be sought. Of these, the opening 

 from the mouth, the opening into the larynx, and the continuation of the 

 cavity into the oesophagus, are single and median. Two paired openings, 

 namely, from the nasal chambers and from the Eustachian tubes, are present 

 in the dorsal part of the cavity. 



Tuba atjditiva [Etjstachu]. — The auditive or Eustachian tube is a 

 short passage leading from the middle ear to the dorsal or nasal part of the 

 pharyngeal cavity. It should be looked for medial to the tensor muscle of 

 the soft palate. That part of the tube which is nearest the middle ear has 

 a bony wall formed by the temporal bone, and opens into the ear by the 

 tympanic opening (ostium tympanicum). The remainder, and greater part, 

 of the tube is provided with a cartilaginous medial and a membranous lateral 

 wall. The pharyngeal end of the cartilage produces a ridge-like projection of 

 the mucous membrane of the pharynx, medial to which the pharyngeal 

 opening (ostium pharyngeum) of the tube will be found. 



Dissection.— The tongue, the pharynx, and the larynx should now be 

 removed, in order that an examination of the last named may be 

 proceeded with. 



Larynx. — The larynx is a tubular organ situated behind the root of the 

 tongue and ventral to the pharynx. On each side and ventrally it is related 

 to the constrictor muscles of the pharynx and to the thyro-hyoid, sterno- 

 thyroid, and sterno-hyoid muscles. The organ is provided with a skeleton 

 of cartilages, upon which muscles act in such a way as to cause variations in 

 the character of the interior. The interior itself is lined by mucous membrane 

 continuous, on the one hand, with that of the pharynx, and, on the other, 

 with the lining of the trachea or windpipe. 



