AND THEIR FUNCTIONS. 127 



marrow is not small in quantity, although an examination 

 of the fractured long bones of lions shows that the cross- 

 sectional areas of their marrow cavities are relatively smaller 

 than those of corresponding bones of the ox, deer, and many 

 other animals. Again, the long bones of the pig have a 

 rather large amount of marrow, e.g., the femoral bones 

 commonly have a marrow cavity more than half an inch in 

 diameter. 



b. Skeletal Structures of Aristotle's Anaima. — Some of 

 the skeletal structures of the Anaima, or animals without 

 blood, are described very briefly in H. A. iv. cc. 1-7, and 

 P. A. iv. c. 5, 



Aristotle speaks of the cuttle-bone of Sepia and the pen 

 of Loligo, saying that each is found in the dorsal part of the 

 body, that the pen is thin and somewhat cartilaginous, that 

 the cuttle-bone is strong and broad, of a nature between 

 that of bone and that of fish-spine, and that it is spongy and 

 friable within.* 



Aristotle's descriptions of the materials of these internal 

 structures is faulty, cuttle-bone being calcareous and the 

 pen horny, but in other respects his statements are substan- 

 tially correct. 



The external parts of crustaceans, he says, are not brittle, 

 but are of a tough nature ; those of his Ostrakoderma, such 

 as snails and oysters, are hard and brittle, and the external 

 parts of his Entoma are neither harder nor softer than their 

 internal parts.! These statements are fairly clear, except 

 with respect to the Entoma, for Aristotle included among 

 these such animals as scorpions, beetles, centipedes, and 

 millipedes, the external parts of which are often very hard. 



He also describes the external coverings of some of the 

 ascidians, saying that they are of a nature between those of 

 skin and shell and can be cut like leather. J 



Aristotle compares the perforated shell of the sea-urchin, 

 when divested of its skin, to a lantern. § 



c. Teeth and Horns. — Aristotle considered the teeth to be 

 very hard bones. He says : "In the jaws are the teeth, the 

 bone of which is partly solid and partly hollow. The bones 

 of the teeth are the only ones which cannot be engraved." || 

 This is clearly a reference to the enamel. 



In several passages Aristotle deals with the relationship 



- E. A. iv. c. 1, s. 12. f Ihid, iv. c. 1, ss. 2 and 3. 



\ Ihid. iv. c. 6, s. 1. § Ihid. iv. c. 5, s. 6. 



II Ihid. iii. c. 7, s. o. 



