198 ELEMENTARY ANATOMY. , [LESS. 



wanting, as in Testtido, or all but wanting, as in the Wombat. 

 It may be very narrow, as in Pteropus. It may be much 

 marked, as in the Ruminants. 



The pit for the origin of the popliteus muscle may be 

 much deeper, and coexist with a similar pit in the external 

 condyle (for the origin of the flexor longus digitorum muscle), 

 which condition, together with the narrowness of the rotular 

 surface, may give the lower end of the femur a peculiar aspect, 

 as in Pteropus. 



The external condyle may present a marked groove sub- 

 dividing it. This is the case in Birds, where this groove 

 serves to receive the head of the fibula. 



Instead of the concavity which exists in man at the pos- 

 tero-inferior part of the shaft (increased through the back- 

 ward projecting of the condyles), this part may be nearly flat, 

 as in Birds. 



Neither tuberosity is ever perforated like the internal con- 

 dyle of the humerus in some Mammals. 



The femur may be only a rudiment even in some Mammals, 



FIG. 169. SKELETON OF RUDIMENTARY PELVIC LIMB OF BOA CONSTRICTOR. 



(After Filrbringcr.) 

 f, rudimentary femur, at the end of which is(/) a minute, triangular, and hook like 



tibia ; i, so-called pubis possibly an enormous ilio-pectineal eminence ; /, 



rudimentary ilium ; p, ischium, or pubo-ischium. 



as e.g. some fin Whales ; and the same may be the case in 

 some Reptiles, as e.g. Lialis Burtonii, Boa, and Stenostoma. 



The PATELLA may be wanting altogether in man's own 

 class, as in the Wombat. It may be very small, as in the Bats 

 and Seals. It may be very narrow in proportion to its length, 

 as in the Agouti ; or extraordinarily large and elongated, as 

 in the Grebe; or represented by two super-imposed ossifica- 

 tions, as in the Ostrich. Every trace of it may be wanting, 

 as in the Frogs and Tortoises. It may be irregular in shape, 

 as in the Bustard and Ostrich. 



13. That important bone of man, the TIBIA, attains a yet 

 greater relative size in very many Vertebrates than it does in 

 him. Like the femur, however, it is not universally present 

 in every class, as it has no distinct representative in Fishes. 



As compared with its fellow leg- bone (the fibula), the tibia 



