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| Location: |
World |
| Subject: |
Morphology - Skull |
| Species: |
All Rhino Species |
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Wall of the middle ear (Paukenh?hle). In an adult, but not old skull of Rhinoceros sumatrensis I found the wall of the middle ear constructed as follows (figs. 61, 62). The small Tympanicum, which is only connected to the long Processus Folii, is very uneven in form. It forms the side-wall of the middle ear through a protuberance which is pointed downwards and forwards, irregularly triangular and thin. It stretches from the edge of the Annulus and lies in the elongation of the plain of the eardrum. The rest of the wall of the middle ear is formed by a high vertical bone, which touches at its upper end on the Pars Petrosa. A part of this bone goes in sagittal direction, parrallel to the plain of the elongation of the Tympanicum mentioned above, and therefore constitutes the inner wall of the middle ear. Behind this part bends sidewards and forms a free protuberance, with a space between this bone and the Petrosum. On the anterior end there is another lateral bend, and the bone takes on a more bended position, and therefore lies in the anterior upper wall of the middle ear and at the side becomes the Tegumen Tympani. Between this bone and the Tegumen tympani one can see a small border, and it is always divided from the Petrosum by a seam. It can be regarded as a Entotympanicum joinred together with the Petrosum.
The back edge of the elongation of the Tympanicum, which is the external wall of the middle ear, lies against the Entotympanicum, which makes that the middle ear is totally closed at the back end. The border is only incomplete due to the space betwen the Entotympanicum and the Petrosum. The lower edges of these two components of the wall only touch each other in the caudal part; more foward there is a small space between them, which is not closed in this skull. The Tuba auditiva must leave the middle ear through this space, which is only bordered by the Tympanicum and the Entotympanicum and probably only through the oral part.
In the literature I could not find any mention of this bone (Lamelle). Huxley (1864) described it, but regarded it as part of the Tympanicum, which would consist of two parts, an anterior one and an interior one (that is the Entotympanicum) and a posterior and exterior one (the Tympanicum itself): ?The tympanic element is very singular;ly formed. It has the shape of a very irregular heap, open above and behind, and much thicker at its anterior superior than at its posterior superior end. The former, irregular and prismatic, is anchylosed with the periotic, just behind and above the auditory labyrinth, it then splits into two divisions, an anterior and inner and a posterior and outer. The anterior, acquiring a thick and spongy texture, curves round to form the front part of the wall of the Tympanum, and then ends in a free, backwardly directed apex, without becoming in any way connected with the periotic, or with the posterior division. The latter, much thinner and denser, curves downwards and backwards in the same way, and also remains free, but its hinder end is prolonged into a flat process, which bends for a short way round the base of the styloid process. The outer wall of the tympanum is therefore very incomplete in the dry skull, opening forwards and downwards, first by the fissure between the anterior branch of the tympani, and the peritic, and secondly, by the cleft between the two divisions of the tympanic' (l.c. p. 255).
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Die Tympanalgegend des Saugetierschadels
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