530 IVORY-BILLED WOODPECKER. 



terminated by a glosso-hyal bone ^ inch in length, but, as already 

 said, has no basal or uro-hyal bone, which, on account of the unusual 

 extent of its motion, would form an impediment. 



From the base of this basi-hyal bone, there proceed backwards and 

 slightly diverging, two slender apo-hyal bones, 1 inch 1 twelfth in length, 

 each of which is continuous with an extremely elongated cerato-hyal 

 bone, 4 inches and 1 twelfth in length, | twelfth in breadth at the 

 commencement, gradually tapering to a blunt point, convex on its 

 lower surface, concave or channelled on the upper, passing under and 

 internally of the articulation of the jaw, and curving upwards along the 

 occiput, until the two meet on the top of the head at the level of the 

 posterior margin of the orbit, in the median line of the cranium, which 

 is much depressed, whence they proceed in mutual contact, inclining 

 slightly to the right side, and terminate a little before the anterior mar- 

 gin of the orbit, half an inch behind the right nostril, and a quarter of an 

 inch from the base of the bill. These prolongations of the os hyoides 

 being of an osseo-cartilaginous texture, are possessed of much elasticity, 

 so as in some measure to resemble a curved spring. 



From near the angle or point of union of the two crura of the lower 

 mandible internally, there proceeds on each side a slender muscle, o o, which 

 running backwards, comes in contact with the prolongation of the hyoid 

 bone at the joint between the apo-hyal and cerato-hyal portions, and is 

 thence continued along the whole extent of the latter, off, og, running 

 chiefly along its upper side, but partially enclosing it, and bound to it 

 by a sheath of cellular tissue, which allows it considerable motion. The 

 bone and muscle are together enclosed in an extremely delicate, tran- 

 sparent, tenacious sheath, moistened internally with a serous fluid, and 

 terminating at the end of the bone, where it is attached by elastic tissue 

 to the cellular substance and periosteiun near the base of the bill. This 

 delicate sheath, perfectly smooth and lubricated on its inner surface, 

 is on the outer attached by delicate filaments to the dense cellular tis- 

 sue which forms a kind of external sheath. It is fixed in its place, 

 and the hyoid bone with its muscle, g g, slides backwards and forwards 

 in it. 



The entire length from the tip of the tongue, c, to the tip of each pro- 

 longation of the hyoid bone at e, is 7 inches 2 twelfths. The protrusion 

 of the tongue is eff'ected by the contraction of the slender muscle above 

 described, o, which having a fixed basis in the lower jaw near its angle. 



:m 



