30 FRINGILLID.E. 



The lower portions of tlie ossa quadrata are pushed somewhat 

 forward by this compression, assisted by two small muscles 

 not exhibited ; but the situation of which may be explained 

 by a reference to figure o. One of these, a small flat muscle, 

 arises from the septum of the orbits behind the small aper- 

 ture observed in the septum, and passes downward to be 

 inserted upon the projecting styloid process of the os quadra- 

 turn ; the second is a small pyramidal-shaped muscle arising 

 also from the septum, anterior to tlie other muscle, and pass- 

 ing downwards and backwards, is inserted upon the omoi- 

 deum, botli muscles by their contraction pulling the os 

 quadratum forwards, and thus elevating the upper mandible. 

 The depressors of the lower jaw, and tlie elevators of the 

 upper jaw, therefore, act together to separate the mandibles. 



To close the mandibles, the temporal and pterygoid mus- 

 cles elevate the lower jaw, assisted by two slender slips, 

 marked d, d, figure 2, which, extending forwards to the su- 

 perior maxillary bones, act in concert by bringing them 

 down. 



When the lateral motion is required, the great pyramidal 

 muscle on the right side pulls the extremity of the lower jaw, 

 to which it is attached backwards ; the pterygoid muscle of 

 the left side at the same time powerfully assisting by carrying 

 that side of the lower jaw inwards. 



Having thus described the muscles of the mandibles in 

 birds generally, and their peculiar mode of action in the 

 Crossbill, I shall quote Mr. Townson's description of the 

 manner in which they are made subservient to the use of the 

 bird in feeding. " The great pine forests, such as the Hartz 

 in Germany, are the natural places of residence of the Cross- 

 beaks, and the seed of the cones of these trees their food, and 

 it is to pull out the seeds from between the squamse, or scales 

 of the cones, that this structure is given them. Their mode 

 of operation is thus : — They first fix themselves across the cone, 



