GLOSSARY 443 



hypothesis. An attempted explanation. 



ichthyopsida. The sub-phylum which includes the fish-like forms — Fishes and 



Amphibia. 

 ichthyopterygimn. The skeleton of the extremity of fishes. 

 ileum. The posterior portion of the small intestine. 

 ilium. The dorsal element of the pelvic girdle. 

 imbricate. A tile- or shingle-like arrangement of alternating parts. 

 immunity. The condition of resistance to infection. 

 impulse, nervous. The change transmitted along an active nerve fiber. 

 incisive canal. The passage in the maxillary bone from the nasal fossa to the mouth 



cavity. 

 incisor. One of the four front teeth of either jaw. 

 incus. The anvil-like middle earbone. 

 infundibulum. The funnel-like portion of the hypothalamus which connects with the 



pituitary gland. 

 inguinal canal. The passage in the groin which contains the spermatic cord, 

 inscriptiones tendineae. Fibrous bands which partially divide the belly of a muscle. 

 insertion. The attachment of a muscle to the bone which it moves. 

 insula. A triangular portion of the cerebral hemisphere covered by the temporal lobe. 

 insulin. The hormone secreted by the islands of Langerhans in the pancreas, 

 integration. The coordination of functions. 

 intercalated. Placed between or interposed, 

 intercostal. Between the ribs. 

 intergrade, sex. An individual with characteristics intermediate between those of the 



sexes. 

 interoceptors. Sense organs in the lining of the alimentary canal. 

 interrenal body. The tissue which in higher vertebrates forms the adrenal cortex, 

 interstitial tissue. The endocrinal tissue of the testis. 

 intestinal portal. The transient embryonic anterior opening of the hindgut and the 



posterior opening of the foregut which appear during the formation of the floor of 



the intestine. 

 intima. The innermost lining of an artery. 

 intrinsic. Situated within a part or organ. 



invaginate. The enclosure of a part by another portion of the same thing. 

 iris. The circular pigmented membrane between the cornea and lens of the eye. 

 ischium. The posterior of the two ventral elements of the pelvic girdle. 

 islands of Langerhans. Endocrinal organs embedded in the substance of the pancreas 



which secrete the hormone insulin. 

 isogamy. The union of similar gametes. 



Jacobson's organ. An accessory olfactory organ which opens into the nasal cavity. 

 jejunum. The middle of the three divisions of the small intestine. 

 jugular ganglion. The "root" ganglion of the vagus nerve. 



keratin. An insoluble protein which forms the base of horny structures. 

 kidney. The chief excretory organ of amniotes. 



Koelliker's pit. The rudiment of the embryonic neuropore of Amphioxus. 

 Krause's corpuscles. Rounded sensory corpuscles located in mucous membranes. 



labial cartilages. Rudimentary cartilages of elasmobranchs. 

 labium. A lip or lip-like structure. 



