94 ANATOMY OF VERTEBEATES. 



into the pterygoid near its articulation with the tympanic. It 

 draws forward the pterygoid bone, wliich pushes against and raises 

 the upper jaw. 



The entotympanicus, or levator tympanicus, arises from the side 

 of the basisphenoid and is inserted into the fossa, on the inner 

 surface of the tympanic bone : in adducting that bone it pushes for- 

 ward the pterygoid, and, consequently, the upper mandible in the 

 same way as the preceding muscle, and assists in opening the bill. 

 The pterygoideus externus arises from the outer side of the 

 orbital process of the tympanic, and is inserted into the mandible in 

 front of the outer articular cavity. The pterygoideiis internus 

 arises by a tendon from the fore part, and by fleshy fibres from 

 the rest, of the depression upon the palatine bone, and is inserted 

 into the inner part of the inflected angle of the mandible. This 

 muscle draws forward the lower jaw. 



In the Cross-bill {Loxia curvirostra) there is a remarkable want 

 of symmetry in the muscles of the jaws on the two sides of the 

 head corresponding to their peculiar position. Those of the side 

 towards which the lower jaw is drawn in a state of rest (which 

 varies in diflerent individuals) are most developed, and act upon 

 the mandibles with a force that enables the bird to dislodge the 

 seeds of the fir-cones, which constitute its food.^ 



The articulation of the lower jaw is strengthened and its move- 

 ments restrained by two strong ligaments ; one of these is extended 

 from the squamosal to the outer protuberance near the joint of 

 the lower jaw. The second ligament extends from the hind end 

 of the squamosal directly backward to the posterior part of the 

 inner articular depression of the lower jaw, and guards against 

 the backward dislocation of the lower jaw. 



§ 133. Muscles of the icings. — Some of those inserted into the 

 humerus, are prodigiously developed, and form the most charac- 

 teristic part of the myology of the Bird. The muscles of the 

 shoulder, however, are but small, and those of the distal segments 

 of the wing still more feeble. 



The Trapezius, fig. 35, 20, arises from the spines of the lower 

 cervical, and a varying number of the contiguous dorsal ver- 

 tebras, and is inserted into the dorsal margin of the scapula and 

 the corresponding extremity of the coracoid. 



The rUomhoideus lies immediately beneath the preceding, and 

 is always single ; it passes in a direction contrary to the trapezius 

 from the spines of the anterior dorsal vertebras to the dorsal edge 

 of the scapula. It has no representative in the Apteryx. 



' XXVI1-. p. 459. 



