956 THE SENSORY APPARATUSES. 



i« also named the guttural duct of the tympanum. It is nearly four inches long 

 in Solipeds, is flattened on both sides, and bordered by the stylo-pharyngeus 

 muscle. Its upper or tympanic orifice is narrow ; the inferior, guttural, or 

 pharyngeal orifice, situated near and behind the guttural openings of the nasal 

 cavities, is wide, and represents a great slit extending obliquely downwards 

 and outwards ; the contiguous borders of this aperture are sustained by a 

 cartilaginous plate — a kind of pavilion formed by the expansion of the tissue 

 •constituting the base of the tube. 



Throughout its length, the guttural duct is cleft inferiorly, and by this 

 long aperture the mucous membrane escapes and descends to form the large sac 

 peculiar to Monodactyles, known as the guttural pouch. 



7. The Guttueal Pouches. 



The mucous membrane lining the Eustachian tube is continuous, forward, 

 with that of the pharynx ; above and behind, it is prolonged into the tympanic 

 cavity, which it lines. Below, it is dilated, and forms the guttural pouch. 



Two in number — one being on each side — the guttural pouches lie against each 

 other in the median plane, and descend to the larynx, where they terminate in a 

 cul-de-sac constituting their fu7idus. Before and behind, they extend from the 

 anterior part of the pharynx to the inferior face of the atlas. The capacity of 

 «ach is about f of a pint ; but in consequence of the extensibility of the mucous 

 membrane, the extent and capacity of the guttural pouches are particularly variable. 



Irregular in shape, like the space which it occupies, the guttural pouch 

 corresponds, behind and above, with the base of the occipital and sphenoid bones. 

 When this reservoir is distended, its lower part, or fundus, descends on the 

 lateral portions of the pharynx and larynx, to the lower extremity of the parotid 

 gland, in the loose connective tissue of that region. 



Externally, the guttural pouch contracts numerous different relations in the 

 intermaxillary and parotideal regions, and in its j^osterior portion. 



a. In the intermaxillary region, it is in relation with the tensor palati, 

 pterygoideus and hyo-pharyngeus muscles, as well as with the internal maxillary 

 artery and lingual nerve ; it envelops the large cornu of the hyoid bone, and 

 covers the inner face of the internal pterygoideus muscle. 



b. In the parotideal region, the guttural pouch responds, above, to the inner 

 face of the parotid gland, from which it is separated by the auricular vessels and 

 nerves ; a httle lower, at the posterior angle of the hyoid bone, to the stylo- 

 hyoideus muscle and the styloid process of the occipital bone ; here the auricular 

 artery passes obliquely upwards and backwards, and the membrane of the pouch 

 is more closely united to the parts covering it. 



Below this, the guttural pouch is in relation with the stylo-maxillaris muscle, 

 external carotid, and the nerves forming the guttural plexus such as the ninth 

 and twelfth pairs, the sympathetic, etc. Lower, it is related to the parotid gland, 

 to the inferior extremity of which it may be prolonged. 



c. Posteriorly. — The guttural pouch is in relation with the atlas, flexor 

 muscles of the head, occipital artery, etc. ; it forms a fold that envelops 

 principally the pneumogastric and sympathetic nerves, and, anteriorly, another 

 fold that encloses the internal carotid. 



The mucous membrane of the guttural pouches is thicker and stronger than 

 that hning the Eustachian tube and the cavity of the tympanum. Only slightly 

 adherent to the adjacent parts, except at the branch of the hyoid, the inner face 



