356 ELEMENTARY ANATOMY. [LESS. 



and in Birds. It may extend almost the whole length of the 

 fibula, as in Phalangista. It may be entirely wanting, as 

 in Bats. 



Besides the muscles which in man connect together the 

 fibula and tibia, two others may exist. One of these, the 

 rotator fibula, is developed in the Lemuroidea. It extends 

 from the back surface of the tibia to the front of the fibula, 

 the fibres passing obliquely downwards and outwards. It 

 lies beneath the popliteus, and its anterior surface is covered 

 by the peroneus longus. 



Another muscle, the fibres of which go in the opposite 

 direction, exists in the Wombat and some other allied 

 forms. It passes downwards from the fibula to the tibia in 

 the place of the interosseous membrane. It is largely deve- 

 loped in the Iguana, Chameleon, and Menopoma, and has 

 been called peroneo-tibial (Fig. 320, PT}. 



The flexor longus digitorum pedis may take origin not 

 only from the leg, but also from the femur, as in Nycticebus 

 and Pteropus ; and it may have mainly a fibular origin, as in 

 the Armadillo and Cape Ant-eater. Even in man's own order 

 (e.g. in Lemur) it may present the singular character of 

 origin from the front of the leg, ascending between the 

 rotator fibulae (before mentioned) above and across the 

 interosseous membrane, so as to be in contact with the pos- 

 terior margin of the tibialis anticus. It may be very much 

 smaller than the flexor longus hallucis, as in the Agouti and 

 Hyrax, and especially in the Virginian Opossum. It may, on 

 the contrary, be very much larger indeed than the other, and 

 have a double origin from the femur, thus indeed forming 

 two muscles, as in Chamaeleo Parsonii (Fig. 316). The gene- 

 rally slight connexion which exists between the tendons of 

 the two long flexors of man is, as it were, a remnant of a 

 far closer connexion existing in other forms, as (in the ex- 

 treme) in the Horse and Tapir, where they unite completely 

 into one tendon, which then again divides, in the latter 

 animal, to form the perforating tendons of the digits. 



The flexor longus pollicis pedis seu hallucis may thus 

 entirely blend with the last-noticed muscle as regards its 

 tendon. On the contrary, as in Cyclothurus, it may be more 

 completely separated from it than in man. It may be entirely 

 absent, or it may be very large as in the Three-toed Sloth. 

 It may be present but send no tendon to the hallux, as in the 

 Orang, in which it springs from the outer condyle. It may 

 appear on the front of the leg, as in Chamceleo Parsonii. It is 



