272 COEVID^. 



the syrinx, which are the real vocal muscles, vary in number 

 in different groups, reaching their maximum in the true 

 Passer es, which have always five pairs. These are represented 

 in their natural position in Figs. 8-10, giving a front, back 

 and side view of these parts in the liaven, while Fig. 11 

 repeats the last but shews three of the five pairs partly 

 displaced to render their superior attachment more obvious. 

 To describe these muscles more particularly it may be said 

 that two pairs of them have a common origin about the 

 middle of the trachea, and, descending on its outside, divide 

 at a short distance above the end of the tube ; one of them 

 — the long posterior tensor (/), being directed downward and 

 backward, is inserted at the extreme posterior end of the 

 first half-ring of the bronchus, while its counterpart — the 

 long anterior tensor (c), passing from the place of separation 

 dovv'nward and forward is inserted below the extreme jjoint 

 of the last ring of the trachea. Within the angle formed 

 by the divergence of each of these pairs, a third slender and 

 cord-like muscle — the sterno-tracheal {d) arises on each side 

 and goes off to be inserted in the sternum. The fourth pair 

 ■ — the short posterior tensor (Ji) is the smallest of all, and, 

 arising near the middle of the lower end of the trachea, 

 its fibres, directed obliquely downwards and backwards, are 

 inserted on the extremity of the first of the incomplete 

 rings of the bronchi. The fifth pair — the short anterior 

 tensor (g) springs like the last from the middle of the 

 trachea, but is somewhat larger and thicker, appearing as 

 though made up of several small muscles in close contact. 

 Its direction is obliquely downward and forward ; it is 

 l)artly hidden by the long anterior tensor (e), and, attached 

 by a broad base to the last ring of the trachea and to the 

 cartilage immediately below, it reaches the extreme end* of 

 the first or second of the bronchial half-rings. 



Thus while the lungs govern the volume of air as well as 

 the force with which it is exj^elled, the syringeal muscles 



* As before stated, in the other great division of Passeres — Prof. Garrod's 

 Mcsonijiodi — none of which are British or even European, such forms as possess 

 muscles that reach to the bronclii, liave their muscles joined to tlie middle and 

 not the extremity of the bronchial half-rings. 



