MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 77 



has a slightly wavy character, as is shown in fig. 291. The 

 configuration of the cartilage at this part renders it possible 

 for the surfaces of the mucous membranes to be immediately 

 applied to one another without any special apparatus, when 

 the cartilaginous lamellse, owing to their elasticity and the re- 

 laxation of the muscles, are approximated. In reference to this 

 point it is to be observed that where a fissure is visible in the 

 middle portions of the tube with high magnifying powers, this 

 is to be clearly distinguished from the oval or semi-cylindrical 

 openings which appear in transverse sections through the 

 upper third beneath the uncinate process of the cartilage. 



The safety tube is well marked in the Cat tribe and in the 

 Horse, Roedeer, Sheep, Goat, Calf, Ox, Rabbit, and Hare. On 

 the other hand, it does not present this form in Monkeys, 

 Marmots, Dogs, Martens, Pigs, and Otters. 



In the Sheep, Stag, Goat, and Calf, there is a delicate series of 

 folds of the mucous membrane on the concavity of the carti- 

 lage, which I described in 1867 and 1868. It does not extend, 

 however, through the whole length of the tube, but is limited 

 to the upper part. The folds are most numerous in the Sheep, 

 Goat, and Calf, whilst in the Ox they have coalesced to form 

 a single projection. 



In the Calf the greatest projection measures from base to 

 apex 0-0420-064 of a millimeter; and in the Ox, 0*080 0'096 

 of a millimeter. From these measurements, then, it appears 

 that the same structure presents considerable differences in 

 relation to the age of the animal, and it is highly probable 

 that the presence of folds at the concavity of the cartilage is 

 intended to facilitate its movements. At the same time we 

 may reasonably admit that they never attain the same size 

 during life as they present in the dead subject. 



In the accessory fissure, where the surfaces of the mucous 

 membrane, when the muscles are not acting, come into contact, 

 numerous regularly opposed folds occur in the pharyngeal 

 segment of the Eustachian tube, which have already been 

 described as they appear in Man by Huschke and F. Arnold. 

 These are also connected with the mechanism of the tuba ; for 

 they are most numerous at that part where the median 

 lamella of cartilage attains its greatest amount of mobility. 



