20 LECTURE II. 



anterior, and now the upper, limbs free to execute the vai-ious pur- 

 poses of the will, and terminated by a hand, which, in the matchless 

 harmony and adjustment of its organisation, is made the suitable 

 instrument of a rational intelligence. 



LECTURE II. 



THE SKELETON. 



Descriptive Anatomy usually commences with the bones, and the 

 consideration of the passive organs of motion before the active ones 

 is conformable to the sequence of development, since the fixed points 

 are formed before the muscular fibres. 



The branch of anatomy which treats of the Skeleton of Vertebrate 

 animals is designated " Osteology," because in anthropotomy it re- 

 lates exclusively to the bones and teeth. But the skeleton, according 

 to its etymological signification of hard and dry parts, might apply to 

 the hair and nails, and, indeed, the entire epidermal system. When, 

 also, in a general survey of the Yertebrata, we see the spinal column 

 gristly in some fishes, and the tendons bony in some birds ; and when 

 we call to mind such homological relations as that of the fibro-mem- 

 branous sclerotic of the human eye with the cartilaginous sclerotic of 

 the turtle and the osseous sclerotic of the cod-fish, it will be obvious 

 that the present branch of anatomy ought naturally to embrace the 

 aponeuroses, ligaments, and cartilages, since these are so many ar- 

 rested stages in the histological develojjment of the internal skeleton. 



In the Invertebrata we saw that the skeleton, or parts analogous * 

 to the bones of the Vertebrata, commonly consisted of large, strong, 

 thick, often unjointed plates, developed in or upon the skin, hardened 

 principally by carbonate of lime, protecting the whole body, and 

 having the muscles attached to the inner surface. 



In the Vertebrata the skeleton chiefly consists of diversely con- 

 figurated, but most commonly cylindrical and articulated pieces, 

 hardened chiefly by phosphate of lime, developed from fibrous and 

 cartilaginous tissue in the interior of the body, of which it forms the 

 internal framework, giving attachment to the muscles by the outer 

 surface, and subserving their action as levers and fulcra. 



The exterior calcified shells and crusts of the Invertebrata are un- 



* For the sense in whieli tlie terms liomologous and analogous are used in the 

 present Lectures, see the Glossary appended to the " Lectures on Invcrtehrata," 

 8vo. 184:3. 



