Functional aspects of musles of the external nose in pigs (Sus scrofa f. domestica)

Abstract

The origin and attachments of the muscles of the external nose were examined in 17 pigs comprising both sexes and different age groups. The modification of the porcine nasal apex to the snout-disc leads to different functional aspects of the muscles of the external nose. Accordingly, all these muscles are attached to the snout-disc. Only the nasolabial levator and caninus muscles are also attached to the upper lip. In addition, the snout-disc includes an intrinsic muscle, the nasal muscle. With regard to morphological and functional aspects, the nostrils can be divided into two parts. The superficial part consists of muscle and connective tissue and is dilated by the cooperative contraction of all muscles of the external nose. In contrast, the second and cartilaginous part of the nostrils dilates less readily, through contraction of the rostrally located deep fibres of the levator nasolabial muscle. As an adaptation for rooting, a special supportive system for muscles of the external nose has developed in pigs, including osseous (eminentia canina) and muscular (muscular slip of the m. levator labii superioris attached to the nasal bone, species-specific development of the m. levator nasolabialis) structures. The observed cartilaginous connection between the ventral lateral nasal and the vomeronasal cartilages suggests another transport mechanism for odours into the vomeronasal organ. Due to this connection, movement of the snout-disc and the cartilages of the external nose could imply passive movement of the vomeronasal cartilage and therefore of the vomeronasal organ.