676 COMPARATIVE ANATOMY 



Hatschek's pit. A preoral pore in amphioxus which opens into the left anterior cavity. 



haustra. Sacculations of the wall of the colon. 



Haversian canal. A bone canal which contains a blood vessel and nerves. 



"heat." Estrus or se.x ardor in animals. 



helix. The margin of the pinna of the ear. 



hemal. Pertaining to the blood. 



hemibranch. The anterior or posterior half of the respiratory portion of a visceral arch. 



hemoblast. A primitive blood cell. 



hemoglobin. The coloring matter of a red blood cell. 



hemopoietic. Blood-forming. 



Henle's loop. A loop of a uriniferous tubule. 



Hensen theory. The theory that nerve fibers are enlarged plasmodesms. 



hepatic. Pertaining to the liver. 



hermaphrodite. An individual with both male and female characteristics. 



hernia. The protrusion of an organ through an abnormal opening. 



heterodont. Having specialized kinds of teeth. 



heterogamy. Reproduction which involves the union of unlike gametes. 



heterolateral. Relating to opposite sides. 



Highmore's antrum. A cavity or sinus of the maxillary bone. 



hilus (hilum). The pit of an organ where blood vessels and nerves enter. 



hindbrain. The posterior of the three primary embryonic brain vesicles. 



hippocampus. A gyrus in the floor of the lateral ventricle which constitutes the greater 



portion of the olfactory centers. 

 histogenesis. The ontogenetic differentiation of a tissue. 

 holobranch. An entire fish gill. 

 homodont. Having teeth all alike. 

 homolateral. On the same side. 



homologous. Having the same structure, development, and relations. 

 hormone. The secretion of an endocrine gland which affects the activity of one or more 



other organs. 

 hyaline. Translucent. 

 hydatid of Morgagni. The rudiment of the Miillerian duct attached to the oviduct or 



testis. 

 hydrostatic organ. An organ of aquatic organisms which serves to adjust internal to 



external pressure. 

 hymen. The membrane which more or less completely closes the external opening of the 



vagina. 

 hyoid. The second visceral arch of vertebrates. The hyoid bone of mammals develops 



from skeletal elements of the second and third visceral arches. 

 hyomandibula. The dorsal element of the hyoid skeletal arch. 

 hypaxial. Ventral to the chief axis. 

 hypertrophy. The abnormal enlargement of an organ. 

 hypobranchial muscles. The muscles ventral to the gills. 

 hypochorda. A transient cord of cells ventral to the notochord. 

 hypocone. A fourth tubercle of a compound tooth. 

 hypodermic. Administered beneath the skin. 

 hypomere. The ventral portion of the mesoderm. 

 hypoparathyroidism. Insufficient secretion of the parathyroid glands. 

 hypophysis. Usually identified with the pituitary gland but strictly forming only the 



anterior lobe of the latter. 

 hypothalamus. The ventral portion of the diencephalon. 

 hypo thenar. The ridge on the ulnar side of the palm. 



