408 DIGESTIVE SYSTEM OF THE HORSE 
guttural pouches. From the Eustachian opening a fold of the mucous membrane 
(Plica salpingo-pharyngea) passes toward but does not reach the aditus laryngis. 
A horizontal fold, the posterior pillar of the soft palate (Arcus pharyngo-palatinus), 
passes along the ventral part of the lateral wall and unites with its fellow over the 
entrance to the oesophagus. The dorsal part of the cavity (Pars respiratoria) 
is lined with a ciliated epithelium, while the ventral part (Pars digestoria) has : 
stratified squamous epithelium. The communication between the two is oval 
Fic. 349.—Posrerior Part oF A Sacrrrau Section oF Heap AND Part or Neck oF Horse, Cur agouT 1 cM. TO THE 
Lerr OF THE MEDIAN PLANE. 
1, Posterior nares; 2, pharyngeel orifice of Eustachian tube; 3, aditus laryngis; 4, aditus cesophagi; 5, posterior 
pillar of soft palate; 5’, junction of 5 with its fellow over entrance to cesophagus; 6, epiglottis; 7, body of thyroid 
cartilage; 8, arytenoid cartilage; 9, 9, cricoid cartilage; 10, true vocal cord; 11, false vocal cord; 12, lateral ventricle 
of larynx; 13, crico-arytenoideus dorsalis; 14, esophagus; 15, external carotid artery; 16, hypoglossal nerve; 17, 
glosso-pharyngeal nerve; 18, great cornu of hyoid bone; 19, Eustachian tube; 20, body of hyoid bone; 21, hyoideus 
tramsversus; 22, ridges of hard palate; 22’, soft palate; 23, septum between frontal sinuses; 24, olfactory mucous 
ital; 27, body of sphenoid bone; 
membrane; 25, sphenoidal sinus; 26, basilar part of occipital bone; 26’, supra-occip’ 
28, pituitary body; 29, chiasma opticum; 30, corpora quadrigemina; 31, thalamus; 32, arachnoid; 33, odontoid 
ligament; 34, posterior auricular muscles. 
and is bounded by the free edge of the soft palate and its posterior pillars; it is 
termed the pharyngeal isthmus. On either side of the aditus laryngis is a narrow 
deep depression, the piriform recess (Recessus piriformis). 
The submucous tissue contains numerous mucous glands (Glandule pharyn- 
gee). In the young subject the lymph follicles are numerous and form a collection 
dorsally and between the Eustachian openings, known as the pharyngeal tonsil 
(Tonsilla pharyngea). 
