GLOSSARY. 735 



Thalamencephalon. The part of the anterior cerebral vesicle which 

 is left after the differentiation of the optic lobes and cerebral 

 hemispheres. 



Thrombosis. The occlusion of a vessel by a local coagulation of the 

 blood. 



Trabeculae. A term used to denote the supporting bars of tissue 

 that pass through some organs, such as those proceeding from 

 the capsule to the interior of the spleen or lymphatic glands. 



Trophic. Eclating to nutrition. 



Trypsin. A ferment in the pancreatic juice which in alkaline solu- 

 tions converts proteids into peptones. 



Tyrosin. A substance formed together with leucin during pancre- 

 atic digestion ; it is also produced by putrefaction of proteids. 



Urachus. The bond of union which at an early period connects the 

 urinary bladder with the allantois in the embryo ; it is subse- 

 quently obliterated in the foetus. 



Vacuoles. Small cavities such as occur in cells. They are supposed 

 to have important functions in many unicellular organisms. 



Vagus. The part of the eighth pair of nerves distributed to the vis- 

 cera of the thorax and abdomen ; it is the great regulating nerve 

 of the vegetative functions. 



Vaso-motor. The name given to the nervous mechanisms control- 

 ling the movements of the muscle-wall of the bloodvessels. 



Villus. A hair-like process. A term applied to the small projec- 

 tions characteristic of the small intestine. They contain blood- 

 vessels and lacteals, and are important in absorption. 



Vitellus. The yolk of the ovum, which in mammals divides com- 

 pletely to form the embryo. In birds only a part divides, and 

 the rest serves to nourish the chick. 



Vorticella. Bell animalcule, a bell-shaped unicellular organism 

 with a rudimentary ciliated mouth cavity and rapidly contractile 

 stalk. 



Wolffian body. An embryonic structure the forerunner of certain 

 parts of the genito-urinary apparatus. 



Zymogen. A peculiar substance existing in the secretion of the 

 pancreas supposed to give rise to the pancreatic ferments. 



