238 THE PIGEON 



(b) The glottis, the opening of the trachea or windpipe, in the floor of the 



mouth and behind the tongue. 



(c) The gullet or oesophagus behind the glottis. 



(d) The internal nares in the roof of the mouth. 



(e) The single Eustachian aperture, a median opening behind the internal 



nares. 



Internal Structure. 



Remove all the feathers from the neck and trunk. Note the short tail or 

 uropygium, with the oil or preen gland on its upper surface ; and also the 

 cloaca, a large transverse opening below the base of the tail. Make a median 

 incision through the skin, along the keel of the breastbone. Reflect the skin 

 off both sides, taking care not to injure the crop, which is under the neck and 

 overlying the trachea. Notice the interclavicular air-sac, between the clavicles 

 and round the lower part of the trachea. The exposed mass of muscle on each 

 side of the keel is the pectoralis major of each side. Detach the pectoralis major 

 of one side from the lower half of the keel and the whole length of the clavicle, 

 and from the lateral part of the breastbone or sternum, by cutting close to these 

 bones. Then reflect the muscle outwards so as to show its insertion on the 

 humerus, by carefully separating it (with the blunt handle of the scalpel) from 

 the deeper muscle of the breast, namely, the pectoralis minor or subclavian, 

 which lies in the angle between the sternum and the keel, and which is com- 

 .pletely covered by the large pectoralis major. Note the large pectoral vein and 

 artery in the lower part of the pectoralis major, and take care not to damage 

 these blood-vessels. 



In a similar way reflect the pectoralis minor, which arises from the upper 

 half of the keel and the inner portion of the sternum ; and notice that its tendon 

 passes through the foramen triosseum (an archway formed by the ends of the 

 coracoid, clavicle and scapula) which serves as a pulley ; and so this muscle, 

 when it contracts, raises the wing. 



The pectoralis major, which depresses the wing, is the largest of the three 

 muscles of flight ; the smallest one is the coraco-brachialis, which arises chiefly 

 from the outer side of the coracoid, and which helps to depress the wing. 



Reflect outwards the corresponding muscles of the other side of the breast 

 in the same way ; and open the abdomen. 



The Skeletal System {part}. 



Note the position of the clavicles, which are united at their lower ends to 

 form the furcula or "merry-thought," and are situated just in front of the 

 sternum. Remove the furcula by cutting through the clavicles as near as 

 possible to their points of attachment. (See the third day's work.) 



Note the coracoids underlying the clavicles, articulating with deep facets 

 on the anterior border of the sternxmi and directed upwards, forwards, and out- 

 wards. Raise the hind part of the sterniun, and cut (with scissors) through its 

 attachment to the ribs (both sides). Cut through the coracoids as far away as 

 possible from the .sternum, and remove the sternum entirely by lifting it up 

 posteriorly and detaching it completely from the underlying tissue. 



Make a sketch of the sternum or breastbone, viewed from the side, to show 



