938 



SYRINX 



supplied by a long branch of the Hypoglossal, or 12th pair of 

 cranial nerves (xii. 2 of diagr. p. 624). A branch descends on 

 either side of the Trachea, being often accompanied along its whole 

 length by thin muscles which extend from the Upper Larynx and 

 the Hyoid apparatus (p. 452) to the Syrinx, and the Syringeal 

 muscles proper are in fact the distal portion of such a long lateral 

 mass as in the majority of Birds is now restricted to the lower 

 third part of the Trachea, and is there separated into a variable 

 number of pairs ; but there are also others which, though belonging 

 to the same category, only act upon the Syrinx indirectly. Of 

 these there is in all Birds one pair, but in Anseres, including 

 Palamedem, two pairs, of slender muscles, which arise at about the 

 beginning of the lower third of the Trachea and are inserted upon 

 the arms of the Furcula or upon the lateral processes of the 

 Sternum (p. 909), or again, but rarely however, on neighbouring 

 soft parts and not upon bones. These are the tracheo-clavicular 

 and sterno-tracheal muscles. 



The proper vocal muscles, being those which are inserted upon 

 the lower end of the Trachea or upon the Bronchi, shew an extra- 

 ordinary amount of modification. Their number varies from one 

 pair to seven, and they are either inserted upon the middle or lateral 

 portion of the bronchial semirings (Mesomyodi, p. 546), or attached 

 to the end of those semirings where they pass into the inner tym- 

 paniform membrane (ACROMYODI, p. 1). The former is morphologic- 

 ally the more primitive condition, and is found in an overwhelming 

 majority of Birds ; while the latter, with few exceptions, is restricted 

 to the OsciNES (p. 659). But there are also other conditions — 

 " Anacromyodian," " Catacromyodian " and " Diacromyodian " — 

 according as these muscles are inserted on the dorsal, the ventral 

 or on both ends of the semirings. Hence the distinction between 

 Oligomyod^ (p. 654) and Polymyod^ (p. 737), depending on the 

 presence of few or many song-nauscles, even if applied to Fasseres 

 only, cannot be maintained, for that group includes forms with any 

 number of pairs from 1 to 7. Nor is the distinction between 

 Mesomyodi and Acromyodi always safe. The Tyrannidx for in- 

 stance are anacromyodian, while the Pipridse and Cotingidx are 

 catacromyodian, and these modifications can be shewn to have 

 been derived (comparatively recently) from the weak mesomyodian 

 and oligomyodian condition which prevails in the majority of the 

 so-called Oligomyodge. On the other hand, the diacromyodian type 

 can only have been developed from a strong muscular basis which 

 could split into a dorsal and a ventral mass. Moreover, there 

 are no Fasseres known to be intermediate between those that are 

 diacromyodian and those that are not. We have therefore to 

 distinguish between 



(1) Fasseres diacromyodi, in which some of the syringeal muscles. 



