386 VERTEBRATE ANIMALS OF THE UNITED STATES 



Interfemoral membrane. The portion of the flying membrane of bats which connects the 



hind legs and includes a part of the tail. 

 Intermaxillaries. The premaxillaries; the middle portion of the upper jaw, except in 



mammals. 

 Intemasals. The plates on a snake's head which connect the two nostrils. 

 Interopercle. The opercular bone between the preopercle and the branchiostegals. 

 Interorbital. The space between the eyes. 

 Interparietal. A median bone sometimes present between the posterior portion of the 



parietals. 

 Interspinals. Spine-like bones inserted between the neural spines in fishes, often for the 



support of the fins. 

 Isthmus. The midventral space lying between the right and the left gill-clefts of a fish. 

 Jugular. Applied to the ventral fins of a fish when they are anterior to the pectorals. 

 Keel. A longitudinal ridge along the middle of a scale or other organ. 

 Keeled. Having a ridge along the middle. 

 Labials. The scales lying along the lips of a snake or lizard. 

 Lamella. A leaf- or plate-like structure. 

 Lamellate. Composed of or provided with lamellae. 

 Lamina. A plate-like process. 

 Larva. A young, immature animal which has not yet acquired the form and appearance 



of the adult. 

 Lateral. Toward either the right or the left side. 

 Lateral line. A sensory line on the lateral surface of most fish, extending usually between 



the head and the tail-fin. 

 Lenticular. Doubly convex. 

 Longitudinal. Lengthwise. 

 Loreal plate. The plate between the eye and the nostril on the head of a snake or a 



lizard, just in front of the preocular when it is present. 

 Limibar. Pertaining to the region of the body between the thorax and the sacrum. 

 Lunate. Crescent-shaped; with the form of the new moon. ■ 

 Mammae. The nipples on the ventral surface of a mammalian female. 

 Mammary glands. The milk-secreting glands of the mammalian female. 

 Mandible. The lower jaw. 



Marginals. The marginal plates of a turtle's carapace. 

 Marsupial pouch. The pouch on the belly of the marsupial female in which the young are 



kept. 

 Marsupium. The marsupial pouch. 

 Mastoid region. The region just behind the ear. 

 Maxilla. The upper jaw. 



Maxillaries. The lateral bones of the upper jaw. 

 Median fins. The unpaired fins. 

 Melanic. The tendency to develop melanism. 

 Melanism. An unusual or abnormal accumulation of black pigment in the integument and 



eyes of an animal; opposed to albinism. 

 Membrane bone. A bone which forms in a superficial membrane and not in cartilage. 

 Meroblastic. Eggs the germinal disc of which alone undergoes segmentation. 

 Metabolism. The sum of all the vital processes of an animal's body. 

 Metachrosis. The attribute of changing the body color under the influence of some 



sensory stimulus. 

 Metameric. Pertaining to the body segments; segmental. 

 Metamorphosis. The developmental changes which go on in a young animal's body up to 



the time when it becomes adult. 

 Molars. The hindermost teeth in the mammalian jaw; crushing teeth of certain fishes. 



