The Labyrinth of Animals (Volume 2); Including Mammals, Birds, Reptiles and Amphibians (Paperback)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: INSECTIVORA THE MEMBRANOUS LABYRINTH OF THE HEDGEHOG As remarked above, the labyrinth of the hedgehog shows evidence of a very ancient type. The cochlea possesses only one and a half whorls, and there is a well-developed perilymph space in the canals. The only other mammals examined in which there are so few turns in the cochlea are the sea-cow, the marsupial mole, and the platypus. The whole organ measures 6.5 mm. from the outermost point on the vertex of the posterior canal to the innermost point on the lowest whorl of the cochlea. The latter has a diameter of 3.0 mm., and the second whorl a diameter of 1.75 mm. The diameter of the tube of the cochlea just in front of the round window is 1.5 mm., and there is no very marked bulging of the floor of the scala tympani in this region, such as is found in many of the mammalia. The aqueduct is short but relatively thick. The slant height of the cochlea measured from the apex to the upper margin of the round window is 2.5 mm. The cochlea is of the flat type, as might be expected from the small number of whorls. The vestibule measures rather less than 2.5 mm. in its longest diameter, and the major axis of the oval window is 1.o mm. in length. Two small otoliths are seen in the c vestibule; these appear as white specks in the photograph. The oval window is kidney-shaped. The aqueduct of the vestibule is comparatively thick, and may be preserved in the process of preparation. It may be seen in the photograph behind the common limb of the posterior and superior canals. No pigment is found in the vestibule. The canals of the hedgehog are comparatively thick, and their perilymph spaces are very well marked. They bear a close resemblance to the canals of some of the monkeys. The superior canal measures 2.75 mm. in intern...