2. _Dorso-lumbar vertebræ_, vertebræ with small lateral processes. 3. _Sacrum_, the ninth vertebra, bearing extra long lateral processes or "arms." 4. _Urostyle_, the last vertebra, lying in the median line, a long, slender, blade-like bone, really formed by the fusion of several vertebræ. _C. Vertebra:--_ 1. _Centrum_, the solid, nearly circular portion. 2. _Lateral process_, one of the paired projections, extending outward on either side. 3. _Neural spine_, the single projection, extending toward the dorsal side. 4. _Neural arch_, formed largely by a connection between the lateral process and the neural spine. The arch above and the centrum below inclose the _neural canal_. _D. Pectoral, or Shoulder, Girdle:--_ 1. _Sternum_, the "breastbone," extending along the median ventral line. 2. _Coracoid_, a heavy bone extending from the sternum sidewise to support the arm. 3. _Clavicle_, the "collar bone," a light bone in front of the coracoid. 4. _Scapula_, the "shoulder blade," a broad, thin bone which arches around to the dorsal side. _E. Pelvic, or Hip, Girdle:--_ 1. _Ilium_, a long, slender, curved bone, with its mate uniting to form an inverted "wishbone"; it is joined to the sacrum. 2. _Pelvis_, the region of the socket at the junction of the ilia. _F. Fore Leg, or Arm:--_ 1. _Humerus_, the single bone of the upper arm. 2. _Radius_, the bone of the lower arm on the thumb side; in the frog united to the ulna. 3. _Ulna_, the bone of the forearm opposite the radius. 4. _Carpals_, small bones of the wrist. 5. _Metacarpals_, a single series of long bones forming the palm of the hand. 6. _Phalanges_, the bones of the fingers and thumb (singular phalanx). _G. Hind Leg:--_ 1. _Femur_, the thigh bone, next to the body. 2. _Tibia_, the larger bone of the lower leg on the inner side; in the frog united to the fibula. 3. _Fibula_, the smaller bone of the lower leg. 4. _Tarsals_, the small bones of the instep. 5. _Metatarsals_, the long bones of the instep. 6. _Phalanges_, the bones of the toes. _Questions._ 1. Whereabouts in the frog has nature made an attempt to inclose delicate or vital structures in bony cases? 2. Examining the inside of the mouth, find the teeth. Judging from their size and structure, of what use are these teeth? 3. What advantages can you see in having the arms and legs attached to girdles instead of having them fastened directly to the vertebral column? How has their development affected the shape of the trunk, as opposed to that of the fish? 4. Make a comparison of the two girdles as to their attachment to the spine and their consequent rigidity or freedom of movement. 5. How many vertebræ are there in the spinal column? What advantage can you see in having the column composed of many small vertebræ instead of a few large ones? Enumerate those having a special form or structure, and state the use of each.