17 



Cutaneous skeletons of the radiated animals Sea stars Sea 

 Eggs, &c. 



Cutaneous skeletons of the annulated animals, worms, insects, 

 &c. 



Similar appearances in more complex animals, snakes, tortoises, 



&c. 



Explanation of the necessity of an internal solid skeleton in the 

 higher class of animals. 



OSSEOUS SYSTEM of Reptiles, Fishes, Birds, Quadrupeds, and 



man. 



Bones always soft in young animals, originally formed of 

 cellular tissue Gelatinous deposit Deposit of gristle or 

 cartilaginous matter Binding of the bones of children 

 The skeletons of certain fishes, and certain parts of the 

 human skeleton always remain flexible Deposit of earthy 

 matter in bone phosphate and carbonate of lime. 

 Manner in which bone is formed in and by the cellular 

 tissue Reticulated structure of the earthy deposit The 

 several deposits shown separately by art Effects of fire 

 and long boiling on bone These agents leave the earthy 

 matter alone Acids reduce bone to the soft and flexible 

 condition of infancy Perfect bone may be reduced to 

 cellular tissue by art. 



Similar changes produced by disease Brittleness of bones 

 Cases Effects of cancer A case Flexibility of bone 

 Rickets. &c., common in Europe Why. 



Generality of the law that all the organs are formed in. and 

 by the cellular tissue Mutual convertibility of organs 

 Ossifications Resemblance of the young of the more 

 perfect animals to adult animals of lower grade Remarks 

 on Youth. 



Structure of joints Necessity for ARTICULAR CARTILAGES 

 Their structure SYNOVIAL MEMBRANES, the serous mem- 

 branes of joints Necessity for LIGAMENTS Their struc- 

 ture Uses Great strength. 



Enveloping membrane of bone, or PERIOSTEUM Explanation 

 of terms PERICHONDRIUM, PERICRANIUM. 

 2* 



