210 THE ESSENTIALS OF HISTOLOGY 



turcica, and is connected with the third ventricle by the infundibulum. 

 It consists of two lobes, a larger anterior, and a smaller posterior. 

 The anterior lobe is originally developed as a hollow protrusion of the 

 buccal epithelium. It consists of a number of tubules, which are lined 

 by epithelium, and united by connective tissue. In some of the tubes 

 the epithelium is ciliated, and sometimes a colloid substance like that 

 occurring in the vesicles of the thyroid has been found in them. 



The posterior lobe of the pituitary body, although developed from 

 the floor of the third ventricle, contains scarcely any perceptible 

 nervous elements in the adult. It consists chiefly of vascular con- 

 nective tissue. 



The membranes of the brain are similar in general structure to those 

 of the spinal cord, p. 185. The dura mater is, however, more closely 

 adherent to the under surface of the bony cavity than is the case in 

 the vertebral canal. The arachnoid is in many places close to the 

 dura mater, and separated by a wide subarachnoid space, which is 

 bridged across by finely reticulating bands of areolar tissue (subarach- 

 noid trabeculae, fig. 246, s.a.} from the pia mater. In the vicinity of 

 the longitudinal sinus, small rounded elevations (arachnoidal villi, 

 Pacchionian glands) project into the dura mater, and even become em- 

 bedded in the skull itself. 



