454 ANATOMICAL TECHNOLOGY. 



examined (§ 1043) ; tlie latter is entocoelian and covered by endyma; 

 the former is wholly ectocoelian (Fig. 122). 



But, along the free border of the fimbria, the velum, or vessels 

 thereof, passes into the procoelia, covered by the endyma, whose 

 attachment may be noted along the entire length of the fimbria (Fig. 

 121). This solution of the continuity of the nervous tissue along 

 the border of the fimbria is the rima (PL IV, Fig. 14, r.), and the 

 intruded border of the velum is the proplexus (PL lY, Fig. 15, ppx.). 



§ 1145. Aula and Porta. — Cut off the larger part of the fornix 

 with the corresponding portion of the callosura, gently push the 

 fornix from the thalamus, and note that, at about the junction of 

 the body with the columna, the adhesion of the velum to both for- 

 nix and thalamus ceases suddenly, and tliat the surfaces of both, 

 ventrad of the adhesions, are covered by the smooth endyma which 

 is characteristic of the coelian cavity. 



So much of the interval between the fornix and thalamus as lies 

 ventrad of the lines of adhesion is the porta. Its ventral limit is 

 formed by the continuity of the two masses (Fig. 123). 



The adhesions coincide with the lines of reflection upon the in- 

 truded velum of the endyma from the columna and thalamus. The 

 slight space mesad of the porta is the aula, and the irregular cavity 

 laterad of the porta is the procoelia, which will be examined later. 



So much of the brain as has not been specified appertains to the 

 prosencephalon. 



§ 1146. Demonstration of the Procoelia, Rhinocoelia and Porta 



("Lateral and olfactory ventricles and Foramen of Monro"). — The 

 procoelia and porta have been incidentally exposed duiing the ex- 

 amination of the encephalic segments. The following directions 

 deal particularly with their parietes and with the continuity of the 

 procoelia with the rhinocoelia. 



Instruments and Materials. — The same as for the examination 

 of the segments (§ 1139). The syringotome is preferable to the tracer. 



For the most satisfactory study of the coelise and the plexuses, 

 the arteries should have been injected with gelatin (§ 1126) and alco- 

 hol thrown into the Foramen infundihuli (§ 1124). The following 

 figures should be consulted before and during the dissection : 117, 

 119-123 ; PL II, Fig. 4 ; PL III, Fig. 13 ; PL IV, Fig. 14, 15, 16, 19. 



§ 1147. Opening the Cella Media of the Procoelia.— A^^\j the 

 edge of the large scalpel along a line 2 mm. dorsad of the main part 



