Guttural Pouches of Horse. 35 



lield firmly in. the fairway of inspii-ation so that descent of the 

 larynx is inhibited by the stylo-hyoid bones. Thus there is no 

 provision outside the (feep tunnel through which pass the larynx 

 and pharynx for expansion of the pharynx during swallowing, 

 etc. Tliis tunnel-space runs into a dome extension in the roof. 

 Down from the auditory tube into the dome of tJie retropharynx 

 these loose folds of pouches extend themselves into a space, 

 which, to borrow an expressive surgical term, may be termed 

 dead space — a space formed by the developed depth of the 

 jaw. In this space, enveloped by the mucous folds and encased 

 by the submucosa, the superior ganglion of the sympathetic, 

 the vagus, the hypoglossal, the glosso-pharvngeal, the spinal- 

 accessory, the mandibular branch of the fifth nerves and the 

 internal and external carotid arteries are found. These struc- 

 tures would, in this position, be damaged against such bodies 

 as the lip of the articular surface of the atlas and the stylo- 

 hyoid bone were it not that these folds endow the nerves and 

 vessels with the power of passive movement during either co- 

 ordinated or erratic muscular action. So freely do these nerves 

 move in the exquisitely delicate submucosa that some difficulty 

 is met in dissecting the pouches owing to the elusiveness of 

 these structures to the forceps. A very importanti function of 

 these pouches is the protection of these basal structures from 

 injuiy. Without the pouches filling the dead space at the base 

 of the skull (the retropharyngeal area) the grace of movement 

 shown in the head and neck of the horse would be lost. They 

 allow of free extension and flexion of the head, by the looseness 

 of the folds with their delicate submucosa adapting themselves 

 and their contained nerves to every movement so beautifullv 

 that nerve pressures or nerve pulls do not arise. 



The air contained within these sacs probably plavs some 

 minor part in lessening the friction of movement by allowing 

 the mucous surfaces to glide over one another with as little 

 friction as occurs between serous surfaces. The guttural 

 pouches represent tissues modified by force operating through 

 the demands of speed and of food having devel<)))ed depth and 

 narrowness at the expense of breadth. 



4\ 



