The maxilloturbinal ridge is also situated in close proximity to the opening of the nasolacrireal canal, by which the nasolacrimal duct enters the nasal cavity.
In extant mammals, the only structures associated with ridges in the lateral portion of the nasal cavity are the respiratory maxilloturbinal and the nasolacrimal duct.
These ridges correspond in location to the maxilloturbinal ridges of extant mammals and are similar to the ridge for the respiratory turbinal of Glanosuchus, described above.
As a result, these ridges more closely match the typical position of the base of the mammalian maxilloturbinal.
The ridges in the anterolateral portion of the nasal cavities of Massetognathus, Trirachodon, and Thrinaxodon closely resemble the basal ridge of the mammalian maxilloturbinal. Their location in the large respiratory chamber, and their association with the nasolacrimal duct strongly suggest that these ridges supported a turbinal structure like that found in extant mammals, with a similar water-recovery function.
These ridges closely resemble the mammalian maxilloturbinal ridges in their anteroventral location, within the respiratory chamber, and in their association to the ostium of the nasolacrimal duct.
However, the maxilloturbinal ridges in therocephalians and cynodonts suggest that ventilation rates in these taxa had increased substantially.
These structures are well situated to modify bulk respired air and probably have a function similar to the mammalian maxilloturbinals, discussed below.
These conditions are met by the respiratory maxilloturbinals, whose function is clearly correlated with the elevated pulmonary ventilation rates of mammals (Hillenius 1992).
The arrangement of these ridges closely resembles the typical pattern in modern mammals and indicates that both respiratory and olfactory turbinates (i.e., maxilloturbinals, and naso- and ethmoturbinals) were present.
Remnants of maxilloturbinals and ethmoturbinals, which indicate that these structures were quite extensive and complex, are described in several specimens.
Because the latter ridges are found on the ascending process of the maxillary bone, Kemp (1969) suggested they may have supported maxilloturbinals. However, these ridges are located behind the internal nares and the transverse choanal process, and it is unlikely that they were involved in modification of respiratory air, as is the case with the maxilloturbinals of modern mammals.