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The innervation of the inner ear has been thoroughly investigated in humans and in some animal models such as the
guinea pig, the rabbit, the cat, the dog, the rat, the pig and some monkeys. Ruminant inner ears are still poorly known
and their innervation was never investigated despite its potential interest in phylogenetic reconstructions. Following
earlier works on the ontogeny of the cow’s ear, we expand our understanding of this structure by reconstructing the fine
innervation pattern of the inner ear of the cow in two ontogenetic stages, at 7 months gestation and at an adult age. Since
we work on dry skeletal specimens, only the endocast of the innervation inside the petrosal bone was reconstructed up to
the internal acoustic meatus. The paths of the facial and vestibulocochlear nerves could be reconstructed together with
that of the spiral ganglion canal. The nerves have a very fibrous pattern. The bony cavities of the ampular and utricular
branches of the vestibulocochlear nerve could also be reconstructed. Our observations confirm that not all bony
structures are present in foetal stages since the branch of cranial nerve VII is not visible on the foetus but very broad on
the adult stage. The fibrous pattern within the modiolus connecting the spiral canal to the cochlear nerve is also less
dense than in the adult stage. The shape of the branch of cranial nerve VII is very broad in the cow ending in a large
hiatus Fallopii; this, together with the above-mentioned particularities, could constitute relevant observations for
phylogenetical purposes when more data will be made available.
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