DISSECTION OF JHE HEAD AND NECK. 187 



intermediate tendon of the digastricus, the larynx, and the submaxillary 

 gland. Besides these, it is related to Stenson's duct and the submaxillary 

 vessels, which have already been dissected on its surface in the inter- 

 maxillary space. 



The Guttural Pouches (Plates 31 and 32). There are two large 

 cavities situated at the base of the skull, above the pharynx, and be- 

 tween the great (styloid) comua of the hyoid bone. Anteriorly they 

 extend as far as the upper margin of the posterior nares, and posteriorly 

 as far as the atlanto-axial articulation. Inwardly the mucous lining of 

 the two pouches forms a mesial partition. Outwardly each pouch has 

 numerous relations, the chief of which are as /follows : — Behind the 

 great cornu the pouch is covered by the subma,xillary gland, and the 

 stylo-maxillaris, digastricus (upper belly), stylo-hyoid, and occipito- 

 styloid muscles, and is crossed by the external carotid, internal carotid, 

 and occipital arteries, and by the 9th, 10th, 11th, 12th, and sympa- 

 thetic nerves. In front of the great cornvi the pouch is covered by the 

 parotid gland and the internal pterygoid muscle, and is crossed by the 

 internal maxillary vessels, the chorda tympani nerve, and the inferior 

 maxillary division of the 5th nerve. The pouch is lined by mucous 

 membrane continuous with that of the Eustachian tube, and by that 

 tube it communicates with the pharynx and the middle ear. Normally 

 the pouch contains air, which it receives from the pharynx through the 

 Eustachian tube. When the mucous lining of the pouch becomes 

 inflamed, pus tends to accumulate in the cavity, since the Eustachian 

 orifice, by which the inflammatory products might escape into the 

 pharynx, is, in the ordinary position of the head, situated towards the 

 upper part of the poucji; ; . ; -. 



The Eustachian, Tube (Plate 32). This is a fibro-cartilaginous tube 

 of three or four inches in length, extending downwards from the petrous 

 temporal bone to the pharynx. At its upper extremity the tube com- 

 municates with the cavity of the middle ear (in the temporal bone), and 

 at its lower extremity it opens into the pharynx by a slit-like aper- 

 ture. For nearly the whole of its extent the tube is slit open along 

 its outer side, and is thus in free communication with the guttural 

 pouch. The tube is lined by mucous membrane, and through its agency 

 air is admitted from the pharynx to the guttural pouch and the middle 

 ear. 



The Internal Maxillaey Artery (Plates 31 and 32) results from the 

 division of the external carotid on the outer surface of the great cornu 

 of the hyoid bone. It is much larger than the superficial temporal, 

 which is the other terminal branch of the external carotid. In passing to 

 enter the subsphenoidal canal, it describes a double or sigmoid curve,— 

 the first convex downwards, the second upwards. In this course the 

 artery is placed within the articulation of the jaw and the external 



