Endoscopic Study of the Oral and Pharyngeal Cavities in the Common Dolphin, Striped Dolphin, Risso's Dolphin, Harbour Porpoise and Pilot Whale: Reinforced with Other Diagnostic and Anatomic Techniques.

Abstract

Simple SummaryDevelopmental studies of the dolphin oral cavity have been scarce and were mostly carried out on adult specimens dealing with teeth and lingual development. Moreover, the adult pharyngeal cavity has been mentioned in cetacean monographic encyclopedias and handbooks. In this work, prenatal and perinatal studies of both the oral and pharyngeal cavities were performed on juvenile and adult specimens to better understand these anatomical structures. Our study analyzes these cavities using high-resolution endoscopy to observe changes in the mucosa and to compare these findings with terrestrial mammals. Even though endoscopy was the main technique used, our study was reinforced with Magnetic Resonance Imaging (MRI), anatomical techniques and fetal histology to locate and identify significant structures. Endoscopy of the oral cavity showed some interesting morphological changes. The incisive papilla, teeth, tongue papillae and lateral sublingual recesses and folds were observed in different development stages. The three different parts of the pharynx (oropharynx, laryngopharynx, and nasopharynx) were examined using endoscopy. The histological study helps us to understand the function of the pharyngeal cavity. The nasopharynx contained important structures such as the orifice of the auditory tube and its expansion, the pharyngeal diverticula of the auditory tubes. This special anatomical area was studied using MRI, serial sections and dissections. Some functional considerations are made about both cavities in the five species of odontocetes studied.In this work, the fetal and newborn anatomical structures of the dolphin oropharyngeal cavities were studied. The main technique used was endoscopy, as these cavities are narrow tubular spaces and the oral cavity is difficult to photograph without moving the specimen. The endoscope was used to study the mucosal features of the oral and pharyngeal cavities. Two pharyngeal diverticula of the auditory tubes were discovered on either side of the choanae and larynx. These spaces begin close to the musculotubaric channel of the middle ear, are linked to the pterygopalatine recesses (pterygoid sinus) and they extend to the maxillopalatine fossa. Magnetic Resonance Imaging (MRI), osteological analysis, sectional anatomy, dissections, and histology were also used to better understand the function of the pharyngeal diverticula of the auditory tubes. These data were then compared with the horse’s pharyngeal diverticula of the auditory tubes. The histology revealed that a vascular plexus inside these diverticula could help to expel the air from this space to the nasopharynx. In the oral cavity, teeth remain inside the alveolus and covered by gums. The marginal papillae of the tongue differ in extension depending on the fetal specimen studied. The histology reveals that the incisive papilla is vestigial and contain abundant innervation. No ducts were observed inside lateral sublingual folds in the oral cavity proper and caruncles were not seen in the prefrenular space.