MOSCULAR SVSTiM 615 
According to the variable configuration of the toes, whether 
two, three or four in number, whether the Bird be anisodacty]l, 
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 Trochilide from the other Cypselomorphe, 
and in the association of the Cathartide with the Alcedinidx, Cora- 
ciidx, Caprimulgidxe and Bucerotidz to the exclusion of Upupa. 
Sundevall! and Garrod? 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. 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 toi., and by the vinculum 
ment most commonly found in 4-toed birds, no matter whether 
the toes be normally placed, paired or reversible: <Ardex, Ciconix, 
Platalea, Gallinx, Ralli, Grues, Rhinochetus, Eurypyga, Otis, Limicolx, 
Pterocles, Columbe, Laridx, Alcidx, Opisthocomus, Cuculidx, Muso- 
phagidx, Psittaci, Striges, Eurylemide. In Herodit 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. iil. 
and iv.—ie. it acts on all. Tendon A goes to ii. iii. and iv. 
Muscles A and P of equal strength. This is the case in Apteryz, 
Tinamidz (Nothura), Spheniscidxe, Steganopodes, Anseres, Colymbi, 
Podicipedes and also in Podica. 
Ill. 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. Naturforsk. 1851, pp. 259-269. 
2 Proc. Zool. Soc. 1875, pp. 339-348. 
3 Thicr-reich, Vogel, p. 195. 
