VEKTEBltATA. 481 



after tlie same type. Both the anterior and posterior limbs, when 

 fully organized, consist of similar parts, most of which are met 

 with in the limbs of the human skeleton. Three bones constitute 

 the shoulder, called respectively the Scapula, the Clavicle, and 

 the Coracoid bone. Three bones in like manner sustain the hinder 

 extremity, the Ilium, the Ischium, and the Pubis ; and these evi- 

 dently represent individually the corresponding pieces found in the 

 shoulder, but differently named. The formation of the limbs is 

 likewise strictly parallel ; a single bone articulates with the osseous 

 framework of the shoulder, or of the hip, called in one case the 

 Humerus, in the other the Femur : two bones form the arm, 

 the Radius and Ulna ; and two likewise enter into the composition 

 of the leg, the Tibia and Fibula : the hand and foot are each 

 supported by a double series of small bones, forming the Carpus 

 of the one and the Tarsus of the other ; and in like manner con- 

 sist of similar pieces, five in number, called the Metacarpal or 

 Metatarsal bones, and of the Phalanges, or joints of the fingers 

 and toes. 



A perfect or typical skeleton must therefore be supposed to 

 consist of all the before-named portions, namely, 1. the cranial 

 and spinal vertebrae ; 2. the face ; 3. an elaborately-formed 

 hyoid framework ; 4. the ribs ; 5. a sternal system of bones, con- 

 stituting, in conjunction with some of the ribs, a thorax ; and 

 Gthly, of four locomotive extremities, made up of the parts above 

 enumerated as entering into their composition. Seldom, indeed, 

 is it that the student will find even the majority of these portions 

 of the osseous apparatus coexistent in the same skeleton ; but, 

 whatever forms of animals may hereafter present themselves for 

 investigation, let the above description be taken as a general 

 standard of comparison, and let all variations from it be considered 

 as modifications of one grand and general type. 



We must, however, proceed one step further in this our prepa- 

 ratory analysis of the skeleton ; and, instead of regarding the indi- 

 vidual pieces of the osseous framework of an adult animal as so 

 many simple bones, be prepared to find them resolvable into 

 several distinct^rts or elements, all or only a part of which may 

 be developed in any given portion of the osseous system. 



In order to simplify as much as possible this important subject, 

 we will select first, what is generally considered as a single bone, 

 one of the most complex vertebra of a fish for instance, and 

 examine its real composition. 



2 i 



