127 



The milk tusks of the dugong have hitherto been mistaken for its 

 permanent tusks, the appearance of which is unknown, since no full- 

 grown skull has hitherto been examined. The grinding teeth differ 

 from those of any other known animal : they consist of a double 

 cone, the external crust of which is not enamel, and covers an in- 

 terior harder coat ; the bulk of the tooth consisting of soft ivory, so 

 that in wearing down, these teeth will be formed into a concave sur- 

 face. 



The organ of hearing presents a peculiarity, says the author, un- 

 known in any other tribe of animals ; the malleus and incus being 

 fastened to the sides of the tympanum by a bony substance extend- 

 ing across the intervening space ; the stapes is opposed to, but not 

 connected with the foramen of the incus ; the handle of the malleus 

 projects in the centre of the circle over which the membrana tym- 

 pani had been spread, so that in the perfect animal it is doubtless 

 attached to the centre of the membrane. 



The habits of the dugong being allied to those of the hippopota- 

 mus, Sir Everard was induced to examine how far this peculiarity of 

 structure might exist in the latter animal ; it is, however, perfectly 

 different, the ossicula in the ear of the hippopotamus being separate, 

 and readily dropping out of the cavity of the tympanum. The ossi- 

 cula of the hippopotamus are small compared with the size of the 

 animal ; but the cochlea makes two turns and a half, which is un- 

 common. The semicircular canals present no apparent peculiarity. 

 In the dugong the semicircular canals are extremely small, as is the 

 cochlea, which only makes one turn and a half. 



The peculiar bony union of the ossicula of the ear with the skull 

 renders it probable that this animal is more indebted for its hearing, 

 than any other that lives in the water, to the vibrations received by 

 the bones of the skull being communicated to the ossicula, and thence 

 to the cochlea and canals. 



Upon the different Qualities of the Alburnum of Spring and Winter- 

 felled Oak Trees. By Thomas Andrew Knight, Esq.F.R.S. Read 

 April 20, 1820. [Phil. Trans. 1820, p. 156.] 



It has long been believed that oak timber felled in winter is su- 

 perior to that felled in spring ; but the cause of the superiority has 

 not been inquired into, and the practice of winter-felling has been 

 discontinued, in consequence of the superior value of the spring 

 bark. 



In the spring of 1817, the author selected two oak trees, not quite 

 a century old, and growing near each other : the one was barked 

 and suffered to remain standing; the other felled, and being im- 

 mediately stripped of bark, was placed in a situation protected from 

 sun and rain. The following December, the other tree, still alive, 

 was cut down, placed in the same situation, and pieces of each, from 

 similar parts, were subjected to the following experiments, at differ- 

 ent subsequent periods. 



