The morphological aspects in case of the malleus in Capreollus capreollus are similar to those described in buffalo (Nourinezhad et al. 2021), donkeys (Nazih 2017), mice (Mohammadpour 2010) and even humans (Pracy et al. 1998). The oval aspect of the head of malleus was reported also in sheep (Simaei et al. 2017) and swine (Pracy et al. 1998) while in cavimorphs, moles and bovids (Argyle and Mason 2008; Simaei et al. 2017) these features are slightly different. The neck of the malleus shows the existence of three visible processes, opposite to the situation found in bovids and buffalo, where this segment is difficult to pinpoint (Nourinezhad et al. 2021). The three processes are noticeable in donkey (Nazih 2017; Gürbüz et al. 2019), rabbit (Kurtul et al. 2003), pig, and humans (Pracy et al. 1998). For the roe deer specimens a worth-mentioning aspect refers to the muscular process, which is evident and conically-shaped (somehow similar to the situation described in buffalo (Nourinezhad et al. 2021)) while in donkey a reduced degree of development of this process is noted (Gürbüz et al. 2019).
The triangular shape of the handle of malleus appears different from the situation found in other ruminants- buffalo, cow and sheep (Nourinezhad et al. 2021).
The incus follows mostly the classical features of the bi radicular molar, with a shorter appearance at the level of the body of the incus. The lenticular process continues the long crus of the incus in medio-lateral direction. Similar facts were reported for goat ossicles (Martonos et al. 2021), dromedary camel (Nourinezhad et al. 2021), rabbit (Kurtul et al. 2003), rat (Li et al. 2015) and chinchilla (Martonos et al. 2019). This individualized piece of ossicle was also reported in some donkey individuals (Nazih 2017) and its absence was cited for sheep fetuses (Simaei et al. 2017)
The stapes is the smallest of the auditory ossicles. It is trapezoidal-shaped, similar to the features of the ossicle described in sheep (Nourinezhad et al. 2021), wolf (Gürbüz et al. 2019) and rabbit (Kurtul et al. 2003) while in other studied species, the ossicle is more like a rectangular piece- buffalo (Nourinezhad et al. 2021), cow (Costeur Loic et al. 2016) and pig (Pracy et al. 1998). Presence of the muscular process was also noted for other species like the donkey, bovids, rabbit, and wolf (Kurtul et al. 2003; Costeur Loic et al. 2016; Nazih 2017; Simaei et al. 2017; Gürbüz et al. 2019) while in humans and sheep fetuses it seems like the structure is just a small rough surface (Isaacson 2014; Simaei et al. 2017). The footplate of the stapes varies much as far as its shape is concerned from species to species. For the roe-deer, we have observed an elliptic shape, somehow similar to the bactrian camel (Bai et al. 2009; Nourinezhad et al. 2021), goat (Martonos et al. 2021), and chinchilla (Martonos et al. 2019). In sheep, this segment is described as almost squared (Nourinezhad et al. 2021).
The middle ear, in its morphology, can be regarded as a pressure amplifier. The ossicular arrangement, its joints, ligaments, and muscles do nothing but change the efficiency of the sound transmission (Huttenbrink 1992; Chhan et al. 2016) and generate mechanical advantage, from the tympanic membrane to the oval window towards the cochlear system (Uziel et al. 2009). The malleus and the incus can be regarded as a type 1 lever that has a counter-clock rotational movement as the tympanic membrane moves inward, pressing then against the internal crus of the stapes onto the oval window, with a cited ratio up to 19:1 effective tympanum to oval window (Pujol 1989). Another term used for the description of this assembly is “hinge-like rotational motion”(Péus et al. 2020) with leveraging capabilities. There is a direct relation between the surface area of the tympanic membrane, the surface of the footplate of the stapes, and the lever system of the middle ear, with a cited ratio between the two arms of the lever of aprox 1.3 (Uziel et al. 2009). By adopting this lever system to the actual measurements, mainly the ones that point to the elements forming the two arms of the lever, we can establish comparative data among related species that have available data (maleo-incal complex and stapes). More than that, some researchers suggest a complex calculation for the expected gain by this hinge-like rotation by multiplying the area ratio between the tympanic membrane (pars tensa) and oval window by the lever ratio of the malleo-incal complex.
A set of measurements (with different reference points) point us to a landmark that is usually not established morphologically but through CT and 3D volume reconstruction procedures- the establishment of the principal axes, the moments of inertia and the C.O.M (Center of mass)(Péus et al. 2020). Our approach did not use this kind of investigation, but due to the high resemblance to the sheep model that sources illustrated and cited, a similar point was established by using the three principal axes suggested (Péus et al. 2020).
To evaluate similarly the available data for the assessment of the lever ratio in the maleo-incal complex we have re-processed the data for sheep (Péus et al. 2017), goat (Martonos et al. 2021) along the ones from roe deer.The compared ratios are among the L manu-L mal, L head-L umbo (for malleus) and the incus the L sp-L lp ratio. As suggested by the comparative figures calculated based on the two distinctive sets of measurements, some interesting facts arose here. The simple calculations of the total lengths of the malleus vs incus show some higher ratio for the goat ossicles, as the ones for sheep and roedeer are not so distant. Values for the length of the long crus of incus as opposed to the length of the stapes are showing higher values for goat, while the pair sheep-roe deer is similar. The malleus vs stapes total lengths are similar in all three compared sets of specimens.
In terms of the measurements used in the assessment of some functional ratios (Péus et al. 2020), a series of facts are revealed. Although the CenterOfMass point was an estimate in our approach for goat and roe deer samples, some figures are pointing to a much clearer differentiation of ratios in the case of the roe-deer data from the ones calculated for sheep and goats. This distinction may be a better indicator for the accuracy of the measurements taken in consideration in direct relation to the functional aspects that point to the mechanics of hearing in these species (lever ratios). Special attention is drawn towards the ratio of length of malleus and the length of the long crus of incus that shows a much smaller ratio for roe deer, as a possible differentiation that might be the result of another pattern in the transmission of vibrations along the complex system of the middle ear.