Page:The Fauna of British India, including Ceylon and Burma (Birds Vol 1).djvu/45

Rh rings are reduced in thickness, leaving wide spaces filled by membrane. The range of sounds produced by this modification is much more limited than in the Tracheo-bronchial syrinx.

In the Bronchial syrinx the voice is produced by modification of the bronchi. But as this type does not occur among the Passeres, its description may be deferred.

It is not the purpose of this survey to pass in review all the anatomical characters which have been used as aids to the classification of this difficult Group, but rather to afford a concise summary of such as are regarded to-day as of importance.

After the syrinx, systematists seem to have relied most upon the plantar tendons of the foot. Sometimes, indeed, too much reliance seems to have been placed upon these; that is to say, a too arbitrary use has been made of the evidence they afford.

Of these tendons two only are specially recognized in this connexion. These are the Flexor profundus digitorum and the Flexor longus hallucis. The first named arises from the greater part of the hinder face of the fibula and tibia, beneath all the other flexors, and at the intertarsal joint passes into a tendon, which, running through a perforation in the metatarsal tubercle, divides just above the distal end of the tarso-metatarsus, sending a slip