Nictitating Membrane 410 166. Muscles of Eyeball 411 167. Diagram of Eye 413 168. Cartilage of External Ear 417 169. Muscles of External Ear 419 170. Tympanic Membrane 422 171. Malleus and Incus 423 172. Stapes 424 173. Membranous Labyrinth 425 ANATOMY OF THE CAT. THE SKELETON OF THE CAT. The skeleton of the cat consists of 230 to 247 bones exclusive of the sesamoid bones (44) and the chevron bones (8). These are divided as follows: head 35-40, vertebral column 52-53, ribs 26, sternum 1-8, pelvis 2-8, upper extremities 62, lower extremities 54-56. The number of bones varies with the age of the individual, being fewer in the old than in the young animal, owing to the fact that in an old animal some bones that were originally separate have united. I. THE VERTEBRAL COLUMN. COLUMNA VERTEBRALIS. The vertebral column, spinal column, or back-bone, consists of a varying number of separate bones, the vertebræ. At its cranial end are seven vertebræ (=cervical=, Fig. 1, _c_) which are without ribs and support the head; caudad of these are thirteen rib-bearing vertebræ (=thoracic=, Fig. 1, _m_); caudad of these are seven that are again without ribs (=lumbar=, Fig. 1, _o_); these are followed by three vertebræ (=sacral=, Fig. 1, _x_) which are united into a single bone, the =sacrum=, which supports the pelvic arch. Following the sacral vertebræ are twenty-two or twenty-three small ribless vertebræ which support the tail (=caudal=, Fig. 1, _y_). [Illustration: FIG. 1.--SKELETON OF CAT. _a_, skull; _b_, hyoid; _c_, cervical vertebræ; _d_, clavicle; _e_, scapula; _f_, sternum; _g_, humerus; _h_, radius; _i_, ulna; _j_, carpus; _k_, metacarpus; _l_, phalanges; _m_, thoracic vertebræ; _n_, ribs; _o_, lumbar vertebræ; _p_, innominate bones; _q_, femur; _r_, patella; _s_, fibula; _t_, tibia; _u_, tarsus; _v_, metatarsus; _w_, phalanges; _x_, sacrum; _y_, caudal vertebræ.]