Shape analysis of fossa masseterica and processus coronoideus in domestic cats (Felis catus) and domestic dogs (Canis familiaris).

Fossa masseterica, to which the musculus masseter is attached, is the pit on the lateral surface of the ramus mandibulae. Processus coronoideus is a protrusion on the upper part of fossa masseterica. Carnivores have a more developed fossa masseterica and a wider processus coronoideus than other species, due to their well-developed jaw muscles. However, there is limited information about the differences of these two structures among carnivorous species. In this study, it was investigated whether fossa masseterica and processus coronoideus differ in shape in domestic cats and domestic dogs. For this purpose, 22 dogs and 20 cats were examined by 3D geometric morphometry. Eighty-one landmarks were used on the fossa masseterica and processus coronoideus. The difference in centroid sizes and shape for cats and dogs was statistically significant (p < 0.0001). PC1 explained 26.47% of the total variance. It was seen that cats and dogs were completely separated according to PC1 results. In cats with a high PC1 value, the processus coronoideus was narrower than in dogs. Also, feline processus coronoideus was more curved than domestic canine processus coronoideus. In addition, the caudal inclination of processus coronoideus was deeper in dogs than in cats. Dogs had a negative PC1 value except for one sample (German Shepherd). The sample with the lowest PC1 value was the French Bulldog (female, 7 years, and 13 kg). Discriminant analysis results showed that the domestic cats and domestic dogs used in the study were completely separated from each other, and this difference was statistically significant. The results of this study showed that dogs with stronger jaw muscles had a deeper fossa masseterica and a wider processus coronoideus than cats.