RAVEN. 77 



back view — and fig. 8, a side view — of the lower portion of the 

 trachea and its muscles in the Raven, which may be consi- 

 dered the type of this form, and from its size admits of clear 

 explanation. Figures 2 and 3 of the second group, page 72, 

 exhibit an outside and an inside view of the same part, but 

 divested of its muscles, to show by the prevalence and inter- 

 position of membrane, the degree of alteration the various 

 muscles are able to effect. 



Referring again to the fourth group, on the opposite page, 

 the pair of muscles which descend on the outside of the trachea, 

 divide at a short distance above the end of the tube, and one 

 portion is directed in continuation downwards and backwards, 

 to be inserted upon the extreme posterior end of the first bone 

 of the bronchia, and is marked f. Its counterpart passes from 

 the place of separation downwards and forwards to be inserted 

 below the extreme point of the last bone of the tube, and is 

 marked e. Within the angle formed by the separation of 

 these two muscles, a third slender and cord-like muscle arises, 

 which goes off to be inserted upon the sternum, as in those 

 birds having one pair ; these are marked d. The fourth 

 muscle, marked h, is the shortest of the five. It arises near 

 the centre of the bottom of the tube, and its fibres, directed 

 obliquely backwards and downwards, are inserted by tendon 

 upon the extremity of the first half-circular bone. The fifth 

 muscle, marked g, arises also from the centre of the tube, 

 similar to the last, but is something longer and thicker, 

 having the appearance of being made up of several small mus- 

 cles in close contact. Its direction is obliquely downwards 

 and forwards, its substance in part hid by the muscle marked 

 e, and it is attached by a broad base to the last bony ring of 

 the tube, to the cartilaginous projection immediately below, 

 and sends one portion to be inserted upon the extreme end 

 of the first bronchial bone. Figure 4 represents these five 

 muscles, three of them being partly detached to render them 



