66 GLOSSARY. 



Hystricomor phae (Gr. hustrix, hustrichos, a hedgehog ; tnorp/it, 

 form). A division of the Rodentia which comprises the 

 porcupine, &c. 



I. 



Ichthyodo'rnlites (Gr. icJithus, a fish ; doru, a spear). The 

 fossil spines or dermal defences of fishes. 



Ichthyopsi'da (Gr. ichthus, a. fish; east's, appearance). The 

 division of the Vertebrata which includes the Amphibia 

 and Fishes. 



Ichthyosau'ria (Gr. ichthus, a fish ; saurus, a lizard). A group 

 of extinct reptiles found in the Mesozoic rocks. 



I'leo-cae'cal valve. A valve guarding the opening by which 

 the ileum communicates with the csecum. 



Ileo-pari'etal band (L. ileum, a division of the intestine ; 

 paries, the walls of a house). A ligament which in the 

 Brachiopoda connects the intestine with the body-walls. 



He'um or Ileum (Gr. eilo, or illo, I twist). The third portion 



of the small intestine. 



Iliac. Relating to the region of the ilium, as the iliac arte- 



. ries. 



lliacus. A muscle passing from the crest of the ilium to the 

 lesser trochanter of the femur. 



llio-/so'as (Gr. psoa, the loins). A muscle arising from the 

 ilium, and inserted into the posterior aspect of the shaft of 

 the femur. 



Ilium (Gr. eileo, I twist). One of a pair of bones in the pelvic 

 girdle, which in the higher Vertebrata forms the upper 

 division of the os innominatum. 



Ima'ginal disks. Masses of indifferent tissue carried by the 

 larvae of some insects when they leave the egg. 



Ima'go (L. an image). The perfect form of insects. 



Imbibition (L. imbfbcre, to drink in). The process of absorp- 

 tion of fluids by organic structures. 



Imbricated (L. imbrex, a roof-tile). Arranged so as to over- 

 lap each other like the tiles of a house. 



Impregnate. To come into contact with an ovum, so as to 

 cause it to germinate. 



Impres'sio colica(L. impression of the colon). A shallow im- 

 pression on the under surface of the liver, which corresponds 

 with the hepatic flexure of the colon. 



