146 GLOSSARY. 



TROCHANTER (rpoxwriip, fr. rpexo, to turn), an outgrowth of bone from the femur 



which affords attachment to the muscles which rotate the thigh. In Man 



there are two, in the Elephant one, in Perissodadyla three. 

 TUBICOLA (tuba, a cylinder; eolo, inhabit), a group of Annelida living in 



calcareous tubes which they form : e. g., Serpulse. 

 TUNICATA (tunica a garment), a synonym of Ascidioida, Mollusks in which the 



shell is replaced by a chitinous test. 

 TURBELLARIA (turbcllse, pi. dim. of turba, a stir), a name applied (from the currents 



caused by their cilia?) to an order of Scolecida, which includes the genera 



Nemertes and Planaria. 

 TYMPANIC (rvij.-ira.vov, a drum), the bone which gives attachment to the membrana 



iympani of the ear, or its homologue. 

 ULNA (coAeVr;), the elbow, hence the bone of the fore-arm which forms the elbow, 



the ciibitus, which answers to the fibula in the hind limb. 

 UMBILICUS (dim. of umbo, a boss), the navel (v. 6^^oA.<5s). 

 UNGUICULATA (unguis, a nail), those animals in which the dorsal part only of the 



digits is covered with horn, forming, if flat, a nail, if curved, a claw. 

 UNGULATA (ungula, a hoof), an order comprising all herbivorous and hoofed 



Mammals, including the Pachydermata and Buminantia of Cuvier, except 



Elephas and Hyrax. 

 UNGTTLIGRADE (ungula, gradior, walk), those animals which walk on the tips of the 



digits only, which are always hoofed, as the horse and ruminants. Cf. DIGI- 



TIGKADE, PLANTIGRADE. 

 URODELA (ovpd, tail ; SrjAoy, visible), an order of Amphibia characterized by the 



tail persisting in the adult state : some are perennibranchiate, others caduci- 



IrancMate ; i.e., in some the gills persist, in others they fall off after the larval 



stage. 

 YACUOLE (menus, empty), an empty space in the sarcode of Rhizopoda and 



Infusoria. 

 VAS DEFEBEXS, "the vessel which carries off" the seminal fluid, the duct of the 



testis. 

 VENTRICLE (ventriculus, dim. of venter, the belly), any hollow space, specially 



applied (as early as Cicero, who has " ventriculus cordis ") to the muscular 



chamber of the heart which pumps blood out of that organ. 

 VERMES (fr. verto, to turn), worms, a name which with Linnseus included Insecta, 



Mollusca, Testacea, Zoophyta, and Infusoria. It is sometimes applied to 



Annuloida generally, but is better restricted to Scolecida. 

 VERTEBRA (verto, to turn), a joint, specially applied to those of the spinal column, 



and thence transferred to the small bones of which it is composed. Hence 



the term Vertebrata, since all animals belonging to this division have a more 



or less developed spinal column. 

 VESICLE (dim. of vesica, a bladder), applied to any sac, but specially to the 



umbilical vesicle and the vesicular seminales. 

 VIBRIO (vibro, to quiver, or vibrate), applie d to minute vegetable organisms which 



are capable of independent movement. 

 VILLUS (a tuft of hair) specially applied to the vascular processes of the cnorion, 



which when fully developed form the foetal placenta. 

 ViTELLrs (the yolk of an egg), present in all forms of ova. The vitelline membrane 



which surrounds it is otherwise called the yolk-sac. 



VOMER (a ploughshare), applied to the bone which helps to form the anterior ter- 

 mination of the cranial axis and the septum narium, from its shape in Man. 



