MUSCULAR SYSTEM 615 



According to the variable configuration of the toes, whether 

 two, three or four in number, whether the Bird be anisodactyl, 

 syndactyl, zygodactyl, heterodactyl, eleutherodactyl or what, the 

 connexion between the two principal deep flexors and their distri- 

 bution to the toes exhibits many modifications, almost any com- 

 bination conceivable occurring in some Bird or other. There can 

 be no doubt that the various uses of the toes running, climbing, 

 grasping, rowing and so on, are the chief determining causes of the 

 manifold arrangements of these tendons. It is easy to understand 

 the action of a single muscle by itself, but of the action of a group 

 of muscles, of their mutual play, and how they partially counteract, 

 supplant or support one another, we know next to nothing. One 

 point, however, is certain, and that is that coincidence does not 

 necessarily indicate affinity. The misconception concerning these 

 plantar tendons has exaggerated their taxonomic value, culminating 

 in the separation of the Trochilidse from the other Cypselomorpha^ 

 and in the association of the Cathartiddz with the Alctdinidte, Cora- 

 ciid&, Caprimulgidse and Bucerotidde to the exclusion of Upupa. 



Sundevall 1 and Garrod 2 have done most to describe the modi- 

 fications of the deep plantar tendons, which are reducible to seven 

 chief types, most of them connected by intermediate stages. 3 In 

 the following enumeration, the muscle and tendon of the flexor per- 

 forans are called A (anterior portion), those of the flexor hallucis P 

 (posterior portion). 



I. Vinculum from P to A. Tendon A splits into 3, going 

 to toes ii. iii. and iv. Tendon P goes to i., and by the vinculum 

 acts also on ii. iii. and iv. i.e. upon all the toes. The arrange- 

 ment most commonly found in 4-toed birds, no matter whether 

 the toes be normally placed, paired or reversible : Ardete, Ciconise, 

 Platalea, Gallinse, Ralli, Grues, Rhinochetus, Eurypyga, Otis, Limicolse, 

 Pterodes, Columbse, Laridx, Alcidaz, Opisthocomus, Cuculidse, Muso- 

 phagidse, Psittaci, Striges, Euryl%mid%. In Eerodii the vinculum is 

 either very weak or wholly lost, thus leading to type VII. 



II. Vinculum very strong and broad, forming the direct and 

 principal continuation of tendon P, of which the hallux receives 

 but a slender portion. Tendon P goes to i. by vinculum to ii. iii. 

 and iv. i.e. it acts on all. Tendon A goes to ii. iii. and iv. 

 Muscles A and P of equal strength. This is the case in Apteryx, 

 Tinamidaz (Nothurd), Spheniscidse, Steganopodes, Anseres, Colymbi, 

 Podidpedes and also in Podica. 



III. Tendons A and P more or less fused throughout the 

 greater extent of the metatarse. The vinculum and the level of 

 the actual crossing are shifted to the distal portion of the meta- 



1 Forhandl. Skandinav. NaturforsTc. 1851, pp. 259-269. 



2 Proc. Zool. Soc. 1875, pp. 339-348. 



3 Thicr-reich, VogcZ, p. 195. 



