730 GLOSSARY. 



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. Relating to nutrition. 

 Trypsin. A ferment in the pancreatic juice which in alkaline solutions 



converts proteids into peptones. 

 Tyrosin. A substance formed together with leucin during pancreatic 



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 subsequently 

 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 viscera 



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



vegetative functions. 

 Vasomotor. The name given to the nervous mechanisms controlling 



the movements of the muscle wall of the blood vessels. 

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



characteristic of the small intestine. They contain blood vessels and 



lacteals, and are important in absorption. 

 Vitellus. The yelk of the ovum, which in mammals divides completely 



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 pan- 

 creas supposed to give rise to the pancreatic ferments. 



