THE MUSCULATURE OF THE TRUNK. 315 



The combined muscle forms a fleshy mass, at the 

 side of the skeleton of the tail ; and it is evident that 

 when the outer fasciculus of the muscle alone contracts, 

 as it may, it will, assisted by an equal force exerted 

 on the part of the corresponding fasciculus of the 

 muscle of the opposite side, tend to powerfully pull the 

 tail feathers apart, and thus spread them. To a certain 

 extent the remaining fasciculi can act in the same 

 way, but they are inserted in such a manner that 

 by their contraction these rectrices will be pulled both 

 downwards and outwards. 



155. The lateralis coccygis is a powerfully developed 

 muscle found immediately beneath the ends of the 

 transverse processes of the caudal vertebrae, and where 

 it is attached to the expanded part of the pygostyle 

 it blends more or less with the muscle of the opposite 

 side, and the two in this region are firmly braced 

 down by a confining, white and glistening, tendinous 

 fascia, which is at once made conspicuous by the 

 removal of several of the muscles described in the fore- 

 going paragraphs. 



The lateralis coccygis arises from the nether aspect 

 of the posterior end of the ilium, and by tendons 

 which severally spring from the under side of the 

 ends of the leading three, occasionally four, caudal ver- 

 tebrae. The combined fibres form a subcompressed 

 muscular mass, directed backwards and slightly inwards, 

 to become attached, on either side, to the posterior mar- 

 gin, exclusive of the midspine, of the expanded portion 

 of the pygostyle beneath. 



This pair of muscles control the lateral movements 

 of the tail and the feathers attached to it, and to 

 some extent its oblique downward movements. 



156. T7ie infracoccygis is that muscle which is 



