Order I. PASSERES. 



The deep plantar tendons passerine ; palate a?githognathous. 



The above two characters in combination suffice to separate a 

 passerine bird from all others. 



The deep plantar tendons are the muscles which run down the 

 leg of a bird and move the toes. There are several types or forms 

 of these muscles. The late Professor G-arrod thus writes about 

 them : 



" In birds generally, whatever the number of their toes, there 

 are two muscles whose fleshy bellies are situated in the leg proper 

 (that is, between the knee and the ankle), deep, and just behind 

 the tibia. These muscles arise, one from almost the whole of the 

 posterior surface of the tibia and from the fibula, in a bipenniform 

 manner, and the other from the inferior surface of the horizontal 

 femur just behind the outer genual articular condyle. The former 

 is termed the flexor perforans digitorum pedis, because its terminal 

 tendons perforate those of the more superficial flexors on their 

 way to the ungual phalanges of their respective toes ; and the latter 

 is termed the flexor longus hallucis, because there is generally a 

 shorter muscle to the same digit. 



" These two muscles descend to the ankle (the joint between 

 the tibio-tarsus and the tarso-metatarsus) side by side ; they run 

 behind it, in the fibro-cartilagmous or osseous mass which, in 

 birds, is always found at the posterior part of the upper end of 

 the tarso-metatarse, in two canals, deeper than any of the other 

 flexor tendons ; and in these canals there is always a definite 

 relation between them. Sometimes the tendons are side by side ; 

 and then it is always that of the flexor longus hallucis which is the 

 external of the two, the osseous vertical ridge, which is nearly 

 always seen in the dry bone, separating them. Sometimes, how- 

 ever, one is superficial or, in other words, posterior to the other. 

 When this is the case, it is always the flexor perforans digitorum 

 which is the deeper. In the Swifts, for instance, ihe, flexor longus 

 hallucis quite covers the flexor perforans digitorum ; but in most 

 Parrots, as may be seen by the disposition of the osseous canals in 

 the dry tarso-metatarse, that for the former muscle is external as 

 well as superficial, only partially covering it. 



" These relations are constant, and must be always borne in 

 mind in all attempts to identify the muscles. From these it can 



