78 THE SURGICAL ANATOMY OF THE HORSE 



the ninth, tenth, eleventh, and twelfth cranial nerves and also by the 

 sympathetic cord. 



In front of the cornu the pouch is related to the internal maxillary 

 vessels and to the inferior maxillary division of the fifth cranial 

 nerve. 



Each pouch is lined by mucous membrane, which is continuous with 

 the mucous lining of the eustachian tube. Since the latter opens into 

 the pharynx there is thus a communication between the guttural 

 pouches and the pharyngeal chamber, and this communication it is 

 important to remember. 



Plate XVIII. shows a transverse section through one of the pouches. 

 On looking into the pouch from below we see a bulging inwards from 

 its outer wall, which is caused by the styloid-cornu of the hyoid bone. 

 On its inner wall is seen the eustachian tube. The probe is passed 

 through the triangle of Virborg. 



In the plate the pouch is in its normal condition, with its wall 

 slightly fallen in on account of the pressure of the surrounding 

 structures. 



On palpating the interior it will be found that the membranous wall 

 is very extensive and distensible, so that when the pouch becomes filled 

 with some material such as purulent matter it easily admits of great 

 enlargement, and consequently its floor approximates much more closely 

 to the region of the angle of the inferior maxilla. 



In Plate III., where a longitudinal section of the head is shown, the 

 inner wall of the right pouch, which comes into apposition with the 

 corresponding wall of the pouch of the other side, is seen. 



Plate XIX. (facing page 80) shows this wall incised and its flaps 

 reflected. One probe is passed from the pouch through the eustachian 

 tube into the pharynx, and the method of communication between the 

 latter and the pouch is distinctly shown. In this same plate the 

 other probe has been passed through the occipito-styloid muscle into 

 the pouch, and it is seen between the styloid cornu of the hyoid 



