A cavern or cavity, esp. an anatomical cavity or sinus
                                                            
                                                     
                        
                                                
                        
                        
                            any nearly closed cavity or chamber, especially one within a bone, such as a sinus
                                                            
                                                     
                        
                                                
                        
                        
                            A fluid-filled space between the follicle cells, the development of which marks the transformation of a tertiary follicle from a secondary follicle. Composes the bulk of the mature, preovulatory follicle (sometimes called the Graafian follicle) and very obvious on transvaginal ultrasound scanning during monitoring of follicular development as dark, "echolucent" spaces within the ovary.
                                                            
                                                     
                        
                                                
                                                     
                        
                        
                            a natural cavity or hollow in a bone 
                                                            
                                                     
                        
                                                
                        
                        
                            Maxillary sinus located in the cheek under the eye adjacent to the ethmoid sinus.
                                                            
                                                     
                        
                                                
                        
                        
                            Greek antron - cave, hence a space in a bone or organ.
                                                            
                                                     
                        
                                                
                        
                        
                            An entry or opening cavity or chamber.
                                                            
                                                     
                        
                                                
                        
                        
                            (Latin = a cave, cavity; a nearly-closed cavity or bulge) In the ovary this refers to the follicular fluid-filled space within the follicle.
                                                            
                                                     
                        
                                                
                        
                        
                            Fluid filled space surrounding follicle
                                                            
                                                     
                        
                                                
                        
                        
                            Large nasal sinus or spaces in maxilla or upper jaw. Function not really understood
                                                            
                                                     
                        
                                                
                        
                        
                            Gr. antron - a cave]. The fluid-filled cavity of a maturing ovarian follicle.
                                                            
                                                     
                        
                                                
                        
                        
                        
                                                
                        
                        
                            In Biology, "Antrum" is a general term for a cavity or chamber which may have specific meaning in reference to certain organs or sites in the body.