90 ANATOMY OF THE DOMESTIC FOWL 



Origin. From the side of the trachea beneath the posterior border 

 of the broncho-trachealis anticus. 



Insertion. Passes downward and backward across the cavity of 

 the chest and is inserted to the inner part of the costal process of the 

 sternum. 



Shape. A delicate cord of fibers. 



Relations.- Internally with the broncho-trachealis muscles. 



Action. A relaxor of the larynx, and hence, of the tympanic 

 membrane. 



THE STERNAL GROUP 



Triangularis Sterni. Location. In the floor of the thoracic 

 cavity. 



Origin. From the entire superior margin of the summits of the 

 costal processes. 



Insertion. The fibers extend upward and backward, dividing into 

 four digitations which cover the inner surface of the three principal 

 sternal ribs, and are inserted to the first four as high as their 

 articulations with the vertebral ribs. 



Shape. Flat and somewhat triangular. 



Relations. Inferiorly with the floor of the thoracic cavity. 



Action. A powerful muscle of expiration. In contracting, les- 

 sens the cubic content of the thorax. 



The Diaphragm (Fig. 47, No. 10; Fig. 33, No. 9). Description. 

 The diaphragm in the domestic fowl is rudimentary. It consists of 

 a thin semi-transparent membrane, situated between and separating 

 the thoracic and the abdominal cavities. It readily conforms to the 

 various organs pressing upon it from each side. On each side are 

 three rudimentary muscles which extend from the vertebral heads of 

 the second, the third, and the fourth sternal ribs. The fibers of 

 these muscles spread out in fan-like upon the diaphragm, and are 

 seen just above the digitations of the triangularis sterni. 



THE ABDOMINAL MUSCLES 



Obliquus abdominis externus Obliquus abdominis internus 

 Rectus abdominis Transversalis abdominis 



Obliquus Abdominis Externus (Fig. 22, No. i). Location. The 

 outermost muscle of the lateral abdominal wall. 



