COMMON CROSSBILL. 19 



jaw, behind the centre of motion, and consequently by their 

 simultaneous contraction raise the point to which they are 

 attached, and depress the anterior part of the mandible. 

 The lower portions of the ossa quadrata are pushed some- 

 what forward by this compression, assisted by two small 

 muscles not exhibited ; but the situation of which may be 

 explained by a reference to figure 3. One of these, a small 

 flat muscle, arises from the septum of the orbits behind the 

 small aperture observed in the septum, and passes down- 

 ward to be inserted upon the projecting styloid process of 

 the os quadratum ; the second is a small pyramidal-shaped 

 muscle arising also from the septum, anterior to the other 

 muscle, and, passing downwards and backwards, is inserted 

 upon the omoideum, both muscles by their contraction 

 pulling the os quadratum forwards, and thus elevating the 

 upper mandible. The depressors of the lower jaw, and the 

 elevators of the upper jaw, therefore, act together to sepa- 

 rate the mandibles. 



To close the mandibles, the temporal and pterygoid 

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

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

 superior 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 assist- 

 ing 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 



c 2 



