THE ANATOMY OF THE RUFFED GROUSE 737 



scapulare is the largest and originates from the internal basal part of the humerus and the 

 adjoining faciae, and passes fleshy along the humerus between the M. deltoides major and the 

 body. Furbringer"" classifies the origin of this head into four types. Bonasa belongs to type 

 3 — "proximale humerale Ankerung". Caput coracoideura consists of a long tendon which 

 originates by a branched tendon from the M. coracobrachialis posterior and M. proscapulo- 

 humeralis. and passes along the ventral surface of the wing to end in a small muscle which 

 expands the secondaries. Caput humerale originates on the dorso-medial surface of the 

 humerus and passes along the medial surface to insert on the olecranon of the ulna. This 

 head is attached to the humerus for its entire length. 



Specialized Structures and Systems 



Syrinx. The syrinx is formed by modification of the junction of the trachea and bronchi, 

 and thus is of the tracheo-bronchial type. The last six tracheal rings are reduced in size but are 

 not vestigial and are complete rings. In the sub-order, Galli, each tracheal ring is fused on 

 the dorsal side and thus does not leave a drum-like area^'". The penultimate ring is somewhat 

 enlarged ventrally to form a small ixi-lcriorlv directed protrusion and dorsallv it is fused 

 with the dorsal plate of the pessulus. The ultimate tracheal ring is fused with the ventral 

 plate of the pessulus but is incomplete dorsally. The first bronchial semi-ring is not attached 

 to the plate of the pessulus but is suspended by the mcmbrana tympaniformis externa. Its 

 dorsal end is free and expanded. The second bronchial ring is attached to the ventral plate of 

 the pessulus and is wider than the first ring. The pessulus is rod-like in form and extends 

 dorso- anteriorly. Its ends are expanded to form a dorsal and a ventral plate. 



The membrana tvmpaniformis externa forms the lateral wall of the syrinx. The mem- 

 brana tvmpanifcji mis interna strctchi's behveen the ends of the bronchial semi-rings. The 

 bronchidesmus is a membrane stretched between the membrana internae of the bronchi. 

 Triangular pieces of cartilage are included within the membrane. 



There are two sets of muscles which move the trachea and syrinx. The M. trachealis set is 

 composed of one muscle, extending along the trachea as far posteriorly as the sixth (last) 

 tracheal ring. Its function is contraction of the trachea. The M. sterno-trachealis set is 

 composed of one muscle on each side of the syrinx. The insertion of each member extends 

 from the penultimate trachael ring anteriorly along the dorso-lateral border of the trachea for 

 about two centimeters. A slip extends posteriorly to cover the dorsal plate of the pessulus. 

 The origin is on the outer lateral process of the sternum. 



Digestive Tract. This is illustrated in figure 80. The mouth cavit) contains the thick 

 muscular tongue, which is broad, short and triangular in shape. On the floor and roof of 

 the mouth are numerous short, hardened sjiines pointing posteriorly. There is a definite 

 row of these surrounding the entrance to the pharynx. The oesophagus is a simple tube 

 extending to the crop. Although Tuttle*^ mentions rudimentary vocal sacs, there is no indi- 

 cation of an extension of the oesophagus related to the production of vocal sound as in 

 Tympanuchus™. 



The crop is a large spherical diverticulum of the oesophagus lying between the divisions 

 of the furculum on the upper part <>f the breast, mainly on the left side. Its opening to the 

 oesophagus has appro\imatelv the same diameter as the oesophagus itself. Gallinaceous birds 

 have a true crop, which is a diverticulum of the oesophagus, rather than a "false crop" 

 formed by the expansion of the oesophagus as found in certain hawks. From the crop, the 

 oesophagus extends as a short tube to the ventriculus. 



