LEPUS CUNICULUS 339 



of accessibility, a trumpet-shaped structure, the external ear or 

 pinna, is developed. This collects the sound waves and conducts 

 them through the meatus to the tympanic membrane. A columella 

 auris is not present, but its place is taken functionally by a chain 

 of auditory ossicles, the malleus, the incus, the os orbiculare and the 

 stapes, by whose agency the vibrations of the tympanum are trans- 

 ferred to the fenestra ovalis and so to the perilymph surrounding the 

 membranous labyrinth. 



The internal ear itself is also much modified. We find, as before, 

 a vestibule relatively small and divided into a sacculus and utriculus. 

 From it come off the three semicircular canals which, while differing 

 somewhat from those in the lower forms, are essentially the same 

 in structure and function. A small duct us endolymphaticus is also 

 present, but it only runs a short distance and then swells out into a 

 small blind enlargement, the saccus endolymphaticus. The most 

 noticeable alteration is in the cochlea. In the frog this is a com- 

 paratively small projection from the wall of the sacculus, while in 

 the rabbit it has developed into a very complicated structure much 

 larger than the vestibule itself. The cochlea is coiled upon itself 

 so as to resemble somewhat a snail shell, and its internal cavity is 

 divided up into three separate compartments by longitudinally 

 running partitions. It is not proposed to enter into a detailed dis- 

 cussion of the histology or anatomy of this structure, but it should 

 be noted that it is probably to be regarded as a highly specialised 

 organ for the appreciation of musical sounds. 



The organs of touch and taste are very similar to those described 

 previously, save that they, too, appear to reach a higher degree of 

 development, and have a characteristic distribution, as we have seen 

 in the case of the latter on the tongue. 



This then concludes the account of the rabbit, which has been 

 taken as a type of the class Mammalia, which is the highest class of 

 animals now living or, so far as we know, has ever lived, and cul- 

 minates in man himself. They are characterised above all by the 

 great development of their brain, and in this, too, man outstrips all 

 other forms. So that before leaving them it will be as well to con- 

 sider this organ in slightly more detail in a larger form than Lepus. 



The Brain of a Mammal the Sheep. 



For the more detailed study of the mammalian brain we 

 may take that of the sheep. It has the advantage of being of a 

 suitable size and readily procurable, also, in so far as we shall treat 

 of it, the structures are fairly typically arranged. For the purposes 

 of dissection it is best to use a brain that has been hardened for some 

 time previously. 



