The Musculoskeletal System: The Skeleton of the Cat

The complex feline skeleton is composed of 244 separate bones. These bones together with cartilage (the connective tissues that bear weight) form the skeletal system of the cat.

The bones can be classified into three broad categories based upon their shape: long, flat, or irregular. If you think about it, you can probably classify most of the bones yourself simply by thinking abou their shape. The bones in the legs, for example, are long bones. These include the radius, ulna, tibia, and fibula. Flat bones can be found if you look at the scapula, skull, or face. Irregular bones are those that doesn't fit in the other categories and include bones such as the metatarsals and metacarpals.

Things get a little more complicated than that, however, because in additional to have three distinct shapes, the bones of the cat also can come in three varieties of ossification: intramembranous, endochondral, and heterotopic. Heterotopic bones occur after birth, usually under disease conditions, and are formed where you wouldn't normally find bone. These formations can be harmless little extra bits of bone or they can be dangerously close to vital organs. In the last case, they would have to be removed.

Endochondral ossification is the process of bone groth in an area previously occupied by cartilage. The cartilage is slowly replaced by bone. Intramembranous ossification is the development of bone under or with in a connective-tissue membrane.

So why is this important? Because most of the bones in the body are formed using the last two processes. The flat bones of the skull are created through intramembranous ossification while the bones at the base of the skull and in the face and trunk are a combination of intramembrous and endochondral ossification. Bone mass, by which I mean the compact bone of the shafts of the long and flat bones, is formed intramembranously. However, bones grow in length through the endochondral process.

What this all means is that the conformation of the cat is solely determined by the relative prominence of each type of bone growth. Which type of bone growth is prominant is usually dependent on the breed. For example, cats which are lean and lithe, such as the Siamese, have more endochondral ossification. Stockier cats such as the British Shorthair have more intramembranous ossification.