174 JAY ARTHUR MYERS 



In the interbronchial region, in immediate relation to the caudal 

 border of the bronchidesmus, numerous folds and pouches are 

 developed. In the mid-line, the dorsal surface of the bronchi- 

 desmus is attached, by means of a thin sheet of fibrous tissue, 

 to the ventral surface of the oesophagus and the dorsal portion 

 of the cephalic part of the pericardium. From these attach- 

 ments this same sheet of tissue extends ventrally, and is further 

 attached to the caudal border of the bronchidesmus, which thus 

 receives additional anchorage by the sheet of tissue also being 

 attached to the ventral portion of the cephalic part of the peri- 

 cardium. From these last named attachments the sheet of 

 tissue extends cephalad in the median plane, and tapers to a 

 narrow cord. The cord, after a short course, again expands, this 

 time to gain attachment along the entire extent of the junction 

 of the ventral surface and the base of the ventral pjTamid of the 

 pessulus. Ventrally this cord and its expanded portions are 

 attached throughout the entire length to a reflection of the 

 fibrous pericardium surrounding the roots of the great vessels 

 of the heart. 



c. Musculature. In general the musculature of the syrinx of 

 birds is composed of intrinsic and extrinsic muscles. Many 

 birds have from three to seven pairs of intrinsic syringeal 

 muscles. The frequent occurrence of these intrinsic muscles 

 has been recognized of value in the classification of birds. 

 Species possessing them are usually songsters. There are some 

 exceptions, however, such as the crow and the jay, which, 

 though possessing these intrinsic muscles, are no longer classified 

 as singing birds. From the syrinx of the domestic chicken the 

 intrinsic syringeal muscles are absent, and hence its voice organ 

 is of course correspondingly simpler. Because of their absence 

 from the syiinx of Gallus domesticus the intrinsic syringeal 

 muscles merit no further description here. 



The principal extrinsic syringeal muscles are the tracheal 

 muscles known as the sterno-tracheales (fig. 2). In the chicken 

 they are well developed muscles which take origin, one on each 

 side, from the antero-lateral process of the sternum. Their 

 fibers are directed obliquely ventrally and cephalad, and reach 



