An anatomical and endoscopic study of the nasopharynx and larynx of the donkey (Equus asinus).

The researchers focused on studying the anatomical structure of the nasopharynx and larynx in donkeys (Equus asinus) using various techniques such as dissection, fibre optic endoscopy, and radiography. The study revealed unique features of the donkey’s airways that could potentially explain differences in their vocalization compared to horses.

Research Methodology

• The team used multiple techniques like anatomical dissection, fibre optic endoscopy, histological procedures, and radiography to examine and describe the larynx and nasopharynx of the donkey.
• This comprehensive approach allowed for detailed and varied observations, helping to outline a complete profile of the donkey’s unique physiology.

Anatomical Comparisons

• Compared to horses, donkeys showed distinct differences in their nasopharynx and larynx.
• Notably, the donkeys had a much deeper pharyngeal recess – the cavity that extends from the orifice communicating with the nasopharynx.
• Additionally, instead of the lateral ventricle found in horses, a shallow depression was found on the rostral (front) face of each vocal fold in donkeys.

Unique Observations in Donkeys

• The study reported significant findings in the anatomy of the donkey’s larynx, specifically the presence of large laryngeal saccules—air sacs located between certain muscles and cartilage that open into the laryngeal cavity.
• These saccules are thought to be controlled by the thyroarytenoideus muscle, which is divided into two parts that presumably manage the saccules’ secretions.
• This structure, and the fact that the airway in the larynx of donkeys is more angular in relation to the nasopharynx than in horses, could explain the unusual characteristics of vocalisation in donkeys.

Further Insights into Vocalisation

• Vocalisation in donkeys was observed to have both an inspiratory (breathing in) and an expiratory (breathing out) component, which may further differentiate it from vocalisation in horses.
• This distinctive vocalisation process could be related to the shape and orientation of the resonance chambers in donkey’s upper airways, which are unique due to their anatomical differences.