MUSCULAR SYSTEM 613 
on the dorsal face of the base of the first phalanx of the hallux. 
Generally best developed in Birds with a large hallux, as Apieryz, 
Gallinx, Accipitres, Steganopodes and Herodii, but yet very small in 
Picus and absent in Psittaci. When the hallux is very small, as in 
Pterocles and many Limicolx, this muscle still exists, and though 
slender is rather long. 
Mm, flexores longi digitorum consist of three principal sets, 
each of which is again divided into several muscles, the hallux 
having one, the fourth toe two, and the third and second toe three 
each, which are conveniently distinguished by the relation to one 
another of their respective tendons. Those that are inserted on 
the base of the first phalanges are perforated immediately above 
the insertion by the tendons of those that are inserted on the 
second and third phalanges, which in their turn are perforated by 
those that are attached to the terminal phalanges—hence there are 
perforati, perforantes et perforati, and perforantes. 
Mm. flexores perforati digitorum ii. wi. iv. These three, of which 
each anterior toe has one, arise in a variable way, either separately 
or partly blended, from almost any part of the region of the knee, 
but especially from the posterior intercondylar space of the femur, 
from its outer condyle, from the ligaments of the knee and patella, 
the proximal part of the tibia and fibula, and lastly from the 
tendon of the m. ambiens (page 11), of which in most cases the m. 
perforatus iti. partly forms the continuation. Each of them be- 
comes a distinct tendon which passes posteriorly over the inter- 
tarsal joint, and piercing the pad above mentioned, runs along the 
plantar groove of the metatarse to be inserted ventri-laterally on 
the base of the first phalanx of the second, third or fourth toe as 
the case may be—their insertion being perforated as before stated. 
The tendon of the m. perforatus iii. may be easily recognized, first 
by its passing the intertarsal joint and the pad the most super- 
ficially, and next by its receiving below that joint the lateral 
distal tendon of the m. peroneus superficialis. 'The tendon of m. 
perforatus it. often passes the pad through a special canal, but in 
Struthio is wholly absent, in conformity with the loss of the corre- 
sponding toe. The tendon of m. perforatus iv. passes the intertarsal 
joint as superficially as that of the third toe, and is often inserted 
on all the four proximal phalanges of the fourth toe. 
Mm. fleaores perforantes et perforati digitorum wi. et ui., with a 
similar origin to the last group, except as regards the m. ambiens 
(page 11). The tendon of the second toe pierces the pad by a special 
canal, and is inserted on the plantar and lateral faces of the base 
of its first or second phalanx, after having perforated that of the 
foregoing and being perforated by that of the following muscle. 
It is absent in Struthio. The tendon of the third toe in many 
Birds receives a vinculum or slip from that of the m. perforatus ti., 
