The skull, which must have consisted of hardened cartilage, exhibits pairs of nasal and auditory capsules, with a gill-apparatus below its hinder part, but no indications of ordinary jaws.
The columellar apparatus, or auditory chain of ossicles (fig.
No importance can be attached to the presence of horns as an indication of affinity between Arsinoitherium and the Amblypoda; and there are important differences in the structure of the skulls of the two, notably in the external auditory meatus, the occiput, the premaxill.ae, the palatal foramina and the lower jaw.
These are a chain of small bones belonging to the first four vertebrae, which are much modified, and connecting the air-bladder with the auditory organs.
The green gland and the structures associated with it in Decapods were at one time regarded as constituting an auditory apparatus.
The South Australian Caloprymnus campestris represents a genus near akin to the last, but with the edge of the hairy border of the bare muzzle less emarginate in the middle line, still more swollen auditory bullae, very large and posterially expanded nasals and longer vacuities on the palate.
Such hallucinations are commonly provoked by crystal-gazing, but auditory hallucinations may be caused by the use of a shell (shell-hearing), and the other senses are occasionally affected.
The family, Chinchillidae, typified by the wellknown chinchilla, includes a small number of South American rodents with large ears and proportionately great auditory bullae in the skull, elongated hind-limbs, bushy tails, very soft fur and perfect clavicles.
They contribute to the formation of the auditory meatus, and of the right and left carotid canals which accompany the eustachian tubes.
By a simple modification, the open pit becomes a solid ectodermal ingrowth, just as in Teleostean fishes the hollow medullary tube, or the auditory pit of other vertebrate embryos, is formed at first as a solid cord of cells, which acquires a cavity secondarily.