722 GLOSSARY. 



Chorda dorsalis. The precursor of the vertebral column of the em- 

 bryo. 

 Chorion. The outer layer of the membranes of the ovum, part of which 



becomes vascular, and helps to form the placenta. 

 Choroid. The vascular coat of the eyeball. 

 Chromatic aberration. The alteration of white light into prismatic 



colors during its passage through an ordinary lens. 

 Chyle. The fluid absorbed from the small intestines by the lacteals. 

 Cilia. Minute vibratile processes which occur on the surface cells of the 



respiratory and many other epithelial membranes. 

 Circumvallate. Large papilla situated at the back of the tongue. 



They are surrounded by a fossa in the walls of which lie taste buds. 

 Cloaca. The common opening of the genito-urinary organs into the 



primitive hind gut of the embryo. The cloaca persists in birds. 

 Colloid. That condition of quasi-dissolved matter in which it will not 



diffuse through a membrane, such as parchment. The opposite of 



crystalloid. 

 Coordination. The adjustment of separate actions for a definite result, 



as when the nerve centres cause various distinct muscles to act 



together and produce complex movements. 

 Cytod. A term suggested to denote a living protoplasmic unit which 



has no nucleus. 



Decidua reflexa. The outgrowth of the uterine mucous membrane 



which surrounds the ovum. 

 Decidua serotina. The part of the modified mucous membrane of 



the uterus in which the fecundated ovum is lodged. 

 Decidua vera. The altered mucous membrane of the uterus, which 



lines that organ during gestation. 

 Deglutition. The net of swallowing. 

 Desquamation. The term used to denote the casting off of the outer 



layer of the skin. 



Dialysis. The diffusion of soluble crystalloid substances through mem- 

 branes such as parchment. 



Diastole. The period of relaxation and rest of the heart's muscle. 

 Dicrotism. The double wave of the arterial pulse. The dicrotic wave 



is seen on the descending part of the pulse curve. 

 Dioptic media. Transparent bodies, such as those parts of the eye 



which so refract the light that images come to a focus on the retina. 

 Distal. A term used to denote a part relatively far from the centre. 

 Ductus arteriosus. A short bond of union between the pulmonary 



artery and the aorta, which, in the foetus, carries blood from the 



right side of the heart into the aorta. 



