2 1 4 ELEMENTAR Y ANA TO MY. [LESS. 



LESSON VI. 



THE INTERNAL SKELETON GENERALLY CONSIDERED, 



I. HAVING now reviewed the parts composing the internal 

 (bony and cartilaginous) skeleton of man, and seen the more 

 remarkable differences which corresponding parts may pre- 

 sent (whether by excess or defect) in other animals, we are 

 in a position to survey the more general relations of the 

 ossified or chondrified skeleton in general, and that of man 

 in particular, and to summarize as follows : 



The human endo-skeleton, with respect to the number and 

 development of its elements, is a very complete one, except 

 as regards the coccygeal and hyoidean parts of it. The former 

 of these aborts in him as in few other Vertebrates ; the latter 

 is less exceptionally defective. 



In contrast to this completeness in man, whole skeletal 

 regions may be quite or all but absent in some other forms, 

 as in Whales and Porpoises, Eels and Serpents. In Serpents, 

 indeed, not only are limbs generally quite wanting, but the 

 hyoidean region aborts much more than it does in man. 



Man's endo-skeleton is highly organized with regard to the 

 mutual relation and adaptation of its parts, though, except as 

 to the opposability of the thumb to the fingers, it is not more 

 perfect in this respect than is that of many beasts. 



With regard to the number of separate bones of which it is 

 composed, when adult, man's skeleton occupies an inter- 

 mediate position ; as, though in many Vertebrates (especially 

 Fishes), the actual number is greater, yet some Vertebrates 

 (as Frogs, Tortoises, and most Birds) have a smaller number. 



Thus, while more of the bones of the skull, as also of the 

 sacral region, become fused together in him than in most 

 forms, yet a smaller number of such bones escape anchylosis 

 in the class of Birds than in man. 



As to the extent of persistent cartilage in the adult condi- 



