[The hypoglossal channel and its contents in the posterolateral access to the petroclival area].

Measurements of the hypoglossal canal: The midpoint of the inner orifice of the hypoglossal canal is on average somewhat over 26 mm away from the opisthion. The distances of the canal centre come to approximately 30 mm, those of the outer canal orifice to 34 mm. The distance of the intracranial pores from each other amounts to 28 xmm. The medial portal for the extracranial pore is on an average 33 mm away from the portal of the opposite side, the lateral 40 mm from the lateral portal of the opposite side. The intracranial pore of the canal for the XII. nerve is situated on an average 13 mm in front of the posterior rim of the occipital condyle, the midpoint of the canal is 15.85 mm in front of this measuring zone, and the exit of the canal 19 mm. Some differences between the sexes and measurements of the postnatal increase of these distances have been included in this investigation. The diagnostic and surgical importance of the hypoglossal canal are discussed.