OSSEOUS SYSTEM. 17 



fibula presents many varieties, and is often very rudimentary. The 

 two bones lie near to each other, but distinct in the Apes, Car- 

 nivore, and Marsupiata. The fibula is generally very strong and 

 thick in the Edentata, especially the Monotremata, where it far ex- 

 ceeds the tibia in length, by a strong process projecting from it supe- 

 riorly. In Orycteropus it has coalesced with the tibia superiorly ; 

 in the Sloths it reaches beyond the tibia inferiorly, and forms an ar- 

 ticulating surface for the astragalus. In the Rodentia, e. g. Dipus, 

 but especially in the Insectivora, as Talpa, Sorex, the fibula is in- 

 dicated below by a distinct line marking where it has coalesced, 

 frequently beyond its lower half, with the tibia, while a complete 

 space remains between the two bones above. In most Cheiroptera, 

 the fibula is reduced to a thin fibro-cartilage, which most frequently 

 does not reach the end of the tibia. In the Horse it exists merely 

 as a short, slender, style-shaped appendage of the tibia. It is for 

 the most part rudimentary in the Ruminantia, where it is repre- 

 sented by a small quadrangular bone, lying inferiorly against the 

 outer side of the end of the tibia. A patella is very generally met 

 with, and is perhaps only wanting in some Marsupiata. It is par- 

 ticularly large in the Edentata and Pachydermata, and small in the 

 Apes. The average number of the bones of the tarsus is seven, 

 as in Man, in the higher orders of Quadrumana, Carnivora, and 

 Marsupiata. The smallest number is found in the Ruminantia j 

 which, as a rule, have five, the astragalus and scaphoid having 

 coalesced : the Giraffe has only a single scaphoid, and altogether but 

 four tarsal bones. The Camels and Solidungula have six (there be- 

 ing two scaphoids) ; the Edentata have mostly seven or eight. In 

 the Ai the Anterior bones of the tarsus have coalesced mutually, and 

 with the metacarpal bones. In the Cheiroptera the os calcis sup- 

 ports a long slender thread-like bone, like a spur, which bounds the 

 alary membrane posteriorly. The os calcis has generally a long 

 process in the Mammalia for the attachment of the tendo-Achillis ; 

 and there is frequently developed in the substance of the latter be- 

 hind this bone a sesamoid ossicle, or kind of petalla, to the calcane- 

 um. The metatarsus is very similar to the metacarpus, consisting in 

 the Ruminantia of a single bone, divided, however, internally into 

 *tvvo cavities, and having, as in the metacarpus, its original separa- 

 tion marked out by an external elongated longitudinal ridge ; there 

 are also, as appears especially in several Cervine animals, two style- 

 shaped bones loosely connected with the metatarsal bone inferiorly, 

 and which support the phalanges of the spur or dew-claws. The 



2 



