544 MANUAL OF ZOOLOGY. 



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. 



The foot consists normally of five toes connected with the 

 tarsus by means of five metatarsal bones, which closely re- 

 semble the metacarpals. In the Ruminant there are only two 

 metatarsals, and these are anchylosed in the adult, and carry 

 two toes. In the Horse there is only one complete metatarsal 

 supporting a single toe. As a rule, the number of digits in 

 the hind-limb or foot is the same as that in the fore-limb or 

 hand ; but this is not always the case. In the Lions, Tigers, 

 Cats, and Dogs, the posterior limb carries only four toes, the 

 innermost toe or hallux being wanting. In the Quadrumana, 

 again, all the five toes are generally present, but the four outer 

 toes are much longer than in Man, and the hallux is shorter 

 than the other toes, arid often opposable to them, so that the 

 foot forms a kind of posterior hand. The hallux is also not 

 uncommonly opposable in other cases. 



The cranial bones are invariably connected with one another 

 by sutures, and in no other examples than the Monotremes 

 are these sutures obliterated in the adult. The differences of 

 opinion which are entertained as to the fundamental structure 

 of the skull are so enormous, that it will be best not to attempt 

 here any detailed description of the skull of the Mammalia, 

 more especially as there is as yet no universal agreement even 

 as to the nomenclature to be employed. It is sufficient to re- 

 member that the skull is composed of a series of bony segments, 

 which are usually regarded as modified vertebrae. The occipi- 

 tal bone carries two condyles for articulation with the first 

 cervical vertebra. The lower jaw is composed of two halves 



