306 THE MYOLOGY OF THE HAVEN. 



of the opposite side, is of a spindle-like form, the 

 longitudinal axis of which is represented by the 

 linea alba ; and its upper and lower apices being re- 

 spectively in the mid-point of the xiphoidal margin 

 of the sternum, and the mid-point of the inter-pubic 

 ligament. In a fresh specimen it is white and glistening, 

 and very characteristic. 



148. The diaphragm (Fig. 75) in the Raven, as 

 in most existing birds, is in a rudimentary condition 

 only, and by no means meets the ends of that muscle 

 as we find it to be the case in Mammalia. It simply 

 consists of a thin, transparent membrane, overlying 

 the peritoneum on the one hand and the pericardium 

 on the other, completely conforming to the forms of 

 the various organs pressing upon it. 



Three rudimentary muscles within the thorax, on 

 either side, play upon this attenuated midriff. These 

 arise from the vertebral heads of the second, third, 

 and fourth costal ribs, and their fibres spread out 

 in a fan-like fashion upon the membrane in question. 

 These three muscles gradually increase in size as we 

 pass from before backwards, and are to be seen just 

 above the extremities of the digitations of the triangu- 

 laris sterni. 



The best way to examine them is to disarticulate 

 the costal ribs of one side from the sternum ; care- 

 fully remove the muscular walls of the abdomen ; pull 

 the ribs away from the sternum, and pull down the 

 abdominal viscera, upon which the diaphragm will be 

 exposed, and the muscles in question at the sides of 

 the thoracic wall easily examined. 



Macgillivray pointed out these muscles for us in his 

 figure showing certain anatomical structures as they 

 exist in Corvus frugilegus, and Coues has kindly re- 



