402 MAMMALIA. 



merely ligamentous attachment. In some Mammals, however, 

 such as the Mole, and many of the Bats, the pubic bones re- 

 main disunited during life. As a rule also, the ossa innomin- 

 ata are firmly united with the vertebral column. In the Ceta- 

 ceans, in which the hind-limbs are wanting, and there is no 

 sacrum, the innominate bones are rudimentary, and are not 

 attached in any way to the spine. 



The only other bones which are ever connected with the 

 pelvis are two small bones 4 which are directed upwards from 

 the brim of the pelvic cavity in Marsupials and Monotremes. 

 These are the so-called " marsupial bones " regarded generally 

 as not forming parts of the skeleton properly so called, but 

 as being ossifications of the internal tendons of the " external 

 oblique" muscles of the abdomen (fig. 336). 



In those Mammals which possess hind-limbs, the normal 

 composition of the member is of the following parts : i. A 

 thigh-bone or femur ; 2. Two bones forming the shank, and 

 known as the tibia and fibula ; 3. A number of small bones 

 constituting the ankle or tarsus ; 4. The " root " of the foot, 

 made up of the " metatarsus ; " 5. The phalanges of the toes 

 (see fig. 271). 



The thigh-bone or femur articulates with the pelvis, usually 

 at a very open angle. In Man it is distinguished by being the 

 longest bone of the body, and by having the axis of its shaft 

 nearly parallel to that of the vertebral column. In most Mam- 

 mals the femur is relatively shorter, and the axis of its shaft 

 deviates considerably from that of the spine, being sometimes 

 at right angles, or even at an acute angle. 



Of the bones of the leg proper the tibia corresponds to the 

 radius in the fore-limb, as shown by its carrying the tarsus ; 

 and the fibula is the representative of the ulna. The articula- 

 tion between the tibia and fibula on the one hand, and the 

 femur on the other, constitutes the " knee-joint," which is usu- 

 ally defended in front by the " knee-pan " or patella, a large 

 sesamoid bone developed in the tendons of the great extensor 

 muscles of the thigh. The patella is of small size in the Car- 

 nivora, but does not appear to be wanting in any except the 

 Marsupials. In many cases the tibia and fibula are anchylosed 

 towards their distal extremities. In the Horse the fibula has 

 much the same character as in Birds, being a long splint-like 

 bone which only extends about half-way down the tibia. In 

 the Ruminants the reverse of this obtains, the upper half of the 

 fibula being absent, and only the lower half present. 



The tibia articulates with the tarsus, consisting in Man of 

 seven bones, but varying in different Mammals from four to nine. 



