Evolutionary Morphology of the Zygomatic Gland and Lacrimal Bulla in Roe Deer ( Capreolus capreolus Linnaeus, 1758 — Mammalia, Cervidae)

Abstract

The dissection of the heads of three adult roe deer ( Capreolus capreolus) provided evidence that this species of the Cervidae, like carnivores, lagomorphs and certain members of the Bovidae, possesses a zygomatic salivary gland. Homology of this salivary gland in ruminants and carnivores is assumed on the basis of its over-all topographic position and the number and course of its excretory ducts. The zygomatic gland of roe deer is a polystomatic gland and amounts to 0.02% of body weight. As in Saiga tatarica and Capricornis crispus (Bovidae), its secretions are predominantly serous. Its slightly alterated position in roe deer (and in bovids) seems to be caused by an evolutionary transformation of orbitotemporal proportions and the formation of a lacrimal bulla, in particular. This is an inflation of the intraorbital portion of the lacrimal bone providing ventral support to the ocular bulb. The lacrimal bulla is a late evolved character and emerges late in ontogeny. Its postnatal development in roe deer is presented. Comparison with the neonatal stage of lacrimal morphology in cattle suggests a similar ontogenetic development in the Bovidae. The adult grysbok ( Raphicerus melanotis, Neotraginae, Bovidae) provides a ‘model situation’ of the primitive character state at the beginning of the evolutionary development of a lacrimal bulla. Zygomatic gland, lacrimal bulla and other structural elements of the ruminant orbitotemporal region provide an example of the interlocked evolutionary transformation of a complex system, the morphological result of which is a multi-layered compromise between several structurofunctional constraints.