144 COMPARATIVE ZOOLOGY. 
esses and neural arch, till finally nothing is left but the 
centrum. They number from 3 or 4 in Man to 270 in 
the Shark. 
Besides the lower jaw, hyoid, and ribs, Vertebrates 
have other appendages to the spinal column—two pairs 
of limbs.” The fore limb is divided into the pectoral 
arch (or shoulder girdle), the arm, and the hand. The 
arch is fastened to the ribs and vertebree by powerful 
muscles, and consists of three bones, the scapula, or shoul- 
der-blade, the coracozd, and the clavicle, or collar-bone. 
The scapula and coracoid are generally united, the latter 
forming a process of the former; and the clavicles are 
frequently wanting, as in the hoofed animals. The hu- 
merus, radius, and ulna are the bones of the arm, the 
first articulating by ball-and-socket joint with the scapu- 
la, and by a hinge-joint with the radius and ulna. The 
humerus and radius are always present; but the ulna may 
be absent. The bones of the hand are divided into those 
of the carpus, or wrist; the metacarpus, or palm; and the 
phalanges, or fingers. The fingers, or “ digits,” range in 
number from 1 to 5. 
The hind limb is composed of the pelvze arch (or hip- 
bones), the deg, and the foot. These parts correspond 
closely with the skeleton of the fore limb. Like the 
shoulder, the pelvic arch, or os innominatum, consists of 
three bones—zlium, zischium, and pubis. The three are 
distinct in Reptiles and in the young of higher animals; 
but in adult Birds and Mammals they become united to- 
gether, and are also (except in Whales) solidly attached to 
the sacrum. The two pelvic arches and the sacrum thus 
soldered into one make the pelvis. The leg-bones consist 
of the femur, or thigh; the ¢7bea, or shin-bone; and the 
fibula, or splint-bone. The rounded head of the femur 
fits into a cavity (acetabulum) in the pelvic arch, while 
the lower end articulates with the tibia, and sometimes 
