Macroscopic anatomy of the auditory tube diverticulum (guttural pouch) in the thoroughbred equine--a silicon mold approach.

Abstract

The characteristics of the equine auditory tube diverticulum (guttural pouches) were studied in detail by the naked eye and silicon mold method. First, we examined the anatomical relationship between the guttural pouches and their associated bones and muscles. Secondly, a silicon mold was fabricated to clarify the three-dimensional aspect of the guttural pouches, paying a special attention to the distribution of major arteries and nerves surrounding it. Thirdly, the volume of the silicon mold was measured by immersing it in water. The guttural pouches are a pair of pouches located dorso-posteriorly to the posterior pharynx. The pouches had a close contact rostrally with the Os sphenoidale, ventrally with the pharynx and the esophagus, and caudally with the Articulatio atlantoaxialis. The left and right guttural pouches had almost the same capacity in each horse. The A. carotis interna, cranial ganglia of cervical nerves and cervical Truncus sympathicus, as well as the N. vagus, N. glossopharyngeus, N. hypoglossus, and Radices spinales of the N. accessorius, were present in the mucosal crease extending from the roof of the guttural pouches towards the middle of the caudal wall. The N. facialis appeared from the Foramen stylomastoideum ran dorsocaudally along the lateral recess. The N. mandibularis appeared from the Foramen lacerum went over the muscular process of an ear bone, ran along the roof of the lateral recess and finally continued with the rostral side of the guttural pouches. Lymph nodes, scattered on the mucosal surface, appeared as tiny indentations with approximately millet seed size on the silicon surface. The capacity of guttural pouches in adult horses (472 +/- 12.4 cm3) was three-fold larger than that in foals (145 +/- 9.4 cm3).