72 Appendix. 



Before proceeding further it will be necessary to explain the way in which these muscles 

 arise. There is a large air-cell, the anterior thoracic ', in which the syrinx and base of the 

 heart are situated. The visceral walls of this cell are so thin that the trachea may, to all intents 

 and purposes, be said to perforate it. Where it does so, the membrane blends with its fascial 

 sheath most intimately ; and it is from the thus formed ring of junction that the long fibres 

 of the syi-ingeal muscles spring. This ring is not a simple horizontal circle of fibrous tissue 

 surrounding the trachea. In its anterior half it is so ; but behind it descends for some distance 

 on each side to a median spot situated below its general level, at a distance beneath it equal 

 to the diameter of the tube itself, to blend at the angle thus formed with a strong fibro- 

 cartilaginous ribbon, which expands below the level of the tracheal bifurcation, to terminate 

 as a membranous covering to the front of the oesophagus. 



From the postero-lateral portion of the horizontiil moiety of the ring just described, and 

 from its descending limb the posterior longitudinal muscle of the syrinx arises on each side, 

 powerful, and in a single mass, of which the longer postero-external fibres, as it descends, 

 differentiate themselves off to form an independent fasciculus, which is inserted into the 

 ]>osterior hooked extremity of the third bronchial semi-ring. The other much larger internal 

 jjortion, composed mostly of shorter and more oblique fibres, is inserted into the posterior 

 triangular surface of the tracheal three-way piece (last tracheal ring), and into the posterior 

 extremity of the first bronchial semi-ring, a few of its tendiuous fibres of termination apparently 

 runnin'' on to the back of the membrane between the first and second semi-ring, and perhaps 

 slightly to the back of the second semi-ring itself, although this last seems to be independent 

 in this respect. 



The comparatively slender musadus sterno-trachealis springs from the lateral surfaces of 

 the four or five tracheal rings above the last two, emerging between the anterior and posterior 

 intrinsic muscles. 



Menura superha, from the above description, is therefore Acromyodian, although not tj^pically 



Oscine. 



Atrichia rufescens presents very much the same arrangement as Menura. There are three 

 modified bronchial semi-rings, the third descending posteriorly, and the second expanded a short 

 distance before it reaches its anterior termination, the anterior longitudinal muscle being there 

 inserted. The posterior muscle, however, does not clearly separate into two before it reaches 

 its points of insertion, which are identical with those in Menura. The lower tracheal rings 

 are different, in that they are not flattened fi-om above downwards ; they retain the characteis 

 of those above them to a great extent. The last forms the characteristic three-way piece. In 

 Plate VII, figs. 4, 5, and 6, these points are clearly seen. 



Atrichia is therefore also acromyodian, although far from being normally Oscine. It 

 would require but little modification in either it or Menura to convert their syringeal muscular 

 masses into more numerous independent muscles. In the Crow, Starling, and most of the 

 other Oscines I have examined, the third semi-ring is the one to which the long anterior 

 muscle runs, the long posterior not going beyond the second. This condition is just reversed 



' Vide Owen's ' Anatomy of Vertebrates,' vol. ii, p. 211. 



