. Text book of zoology. Zoology. Glass 6. Mammalia. 481 over the outer surface of the eyeball when this is withdrawn into the orbit and covers it partially or entirely. Sometimes {, in Man) it is rudimentary. The sclerotic consists of connective tissue without cartilage* or bone; in some Mammalia, especially in the Whales, it is very thick. In the choroid coat there is frequently a peculiar greenish, blue, or whitish, shimmering membrane varying somewhat in structure, the tape turn [, in the Horse, Rumiaants, Oarnivora). The form of the pupil varies, it is either circular {, in Man
. Text book of zoology. Zoology. Glass 6. Mammalia. 481 over the outer surface of the eyeball when this is withdrawn into the orbit and covers it partially or entirely. Sometimes {, in Man) it is rudimentary. The sclerotic consists of connective tissue without cartilage* or bone; in some Mammalia, especially in the Whales, it is very thick. In the choroid coat there is frequently a peculiar greenish, blue, or whitish, shimmering membrane varying somewhat in structure, the tape turn [, in the Horse, Rumiaants, Oarnivora). The form of the pupil varies, it is either circular {, in Man,), or a perpendicular (Cat, Fox), or horizontal sht (Horse, Ruminants). Auditory organ. The cochlea of Monotremes is like that of Crocodiles and Birds; in all other Mammalia, however, it is much longer and is spirally coiled. As in Keptiles there is a fenestra ovalis and a fenestra rotunda. The single ear- Pig. 392. Diagrammatic trans- verse section of the head of a Mammal, to show the relations of the auditory organ; (the labyrinth is drawn propor- tionally much too large, etc.). a ampuUa, 6 semi-circular canal (only one is represented) c cochlea ; sa saoculus, M utriculus (together forming the vesti- bule) ; round the labyrinth the cavum perilymphatioum, black in the figure, fc bones of the skull, % malleus, am incus, s stapes, t tympanic cavity, r fenestra rotunda, e Eustachian tube, ir tympanic membrane, g external auditory meatus, o external ear. — Orig. (with partial use of older figures).. bone of Reptiles is broken into three, the malleus, which is connected with the tympanum, the incus," and the stapes, the terminal disc of which closes the fenestra ovalis ;t in the Monotremes it consists of a plate and a single shaft; which is usually broader and perforate in other orders, so that the ossicle becomes like a stirrup. The presence of an external meatus is characteristic of the Mammalia; the pit, at the base of which the tympanum is situated in Reptiles, has beco
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
