COMPOSITION OF THE SKELETON. 609 



(1625.) Behind the hyoid apparatus, other arches are attached to the 

 transverse processes of the spinal vertebrae, called ribs ; and the study 

 of these appendages to the spine is one of the most interesting points 

 in the whole range of osteology. In Fishes, wherein respiration is 

 effected entirely by the movements of largely-developed hyoid bones, 

 the ribs are mere immoveable derivations from the transverse processes of 

 the vertebrae, and serve exclusively for the attachment of muscles. In 

 Reptiles, respiration is still accomplished by the os hyoides ; and the 

 ribs, thus performing a secondary office, become convertible to different 

 uses, and assume various forms and proportions. In the Amphibious 

 Reptiles, the most nearly approximated to Fishes, they either do not 

 exist at all, as being needed neither for respiration nor locomotion, or 

 they are represented by minute and almost imperceptible rudiments 

 appended to the extremities of the transverse processes of the vertebrae. 

 In Serpents, the ribs are wanted for locomotion, and are accordingly 

 developed from the head nearly to the tail, forming a series of strong 

 arches, articulated at one extremity with the vertebral column by a very 

 complete joint, but at the opposite extremity they are loose and uncon- 

 nected. In proportion, however, as the hyoid bones, with the larynx, 

 of which they form an important part, become converted into a vocal 

 apparatus (as they gradually do), the ribs, assuming more complete de- 

 velopment in a certain region of the spine, and being augmented by the 

 addition of a sternal apparatus, form a complete thoracic cavity, and 

 thus become the basis of those movements of the body which in hot- 

 blooded animals are subservient to respiration. 



(1626.) The next additions required to complete the skeleton are two 

 pairs of locomotive limbs, representing the legs and arms of Man. In- 

 finitely diversified as are these members both in form and office, they are, 

 when philosophically considered, found to be constructed after the 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 respect- 

 ively 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 evidently 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 said, 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 consist of similar pieces, five in number, 

 called the metacarpal or metatarsal bones, and of the phalanges, or 

 joints of the fingers and toes. 



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