Comparative Anatomy of the Nasal Cavity in the Common Dolphin Delphinus delphis L., Striped Dolphin Stenella coeruleoalba M. and Pilot Whale Globicephala melas T.: A Developmental Study

Abstract

Our goal was to analyze the main anatomical structures of the dolphin external nose and nasal cavity from fetal developmental stages to adult. Endoscopy was used to study the common development of the external nose and the melon, and nasal mucosa. Magnetic resonance imaging (MRI) and anatomical sections were correlated with anatomical sections. Computed tomography (CT) was used to generate 3D reconstructions of the nasal bones and nasal cavities to study its development. Dissections, histological and pathological studies were carried out on the nasal mucosa to understand its function. These results were compared with the horse. Endoscopy showed an external nose with two lips and the upper lip is divided by a groove due to the nasal septum and an obstruction of right nasal cavity was diagnosed in a newborn. Two diverticula (air sacs) were found in the nasal vestibule and an incisive recess (premaxillary sac) in the nasal cavity. These findings were corroborated by 3D reconstructions of the nasal cavities, MRI, anatomical sections and dissections. The presphenoid and ethmoid bones were fused at early stages of fetal development. The ethmoid is the last bone to ossify in the nasal cavity.

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

“…The small grooves may, in fact, be the location of the hitherto unveiled taste receptors [10]. We did not locate receptors for taste or olfaction in the oral or nasal cavity [3].…”

“…The monostomatic salivary glands are absent in cetaceans [ 3 ]. Stomas opened along the lateral sublingual folds (polystomatic gland) and major sublingual and mandibular ducts, with the latter atrophied in cetaceans, as we have observed in histology ( Figure 14 ).…”

“…Tooth formation occurs below the gums [ 3 ]. The final eruption takes place during the perinatal period after lactation (this, along with the few development of the incisive teeth, protects the mother’s nipple), probably by the scratching of the gums against the rough surfaces of food.…”

“…In cetaceans, the lips are tightly sealed, so the mouth is hermet- The oral vestibule in terrestrial mammals could be sub-divided in oral and labial vestibules, due to the presence of a space between lips and teeth (labial vestibule), and between cheeks and teeth (buccal vestibule). In cetaceans, which lack cheeks and, therefore, masseter muscles during development [3], only the labial one is present.…”

“…The oral cavity is not the most studied region in the cetacean head, when compared, for example, with the nasal cavity [ 3 , 4 , 5 , 6 , 7 , 8 ]. The snout is a sensitive anatomical structure, the first one to have contact with the environment and it performs specific interactions, such as courtship (epicritic tactile sensibility) and defence (protopathic tactile sensibility).…”