HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM OF THE WEDDELL SEAL. 155 



a large anterior lobe, a narrow but well-defined intermediate part, and a posterior lobe ; 

 the hinder portion of the intermediate mass is bent at an angle upon the rest of that 

 part, so as to come to lie posteriorly between the lower limit of the posterior lobe 

 and the projecting posterior part of the anterior lobe. From the surface, the upper 

 part of the posterior lobe appears wedge-shaped and folded over the hinder part of 

 the anterior lobe .so as to cover about a third of the upper surface. 



The atypical tissue on the upper surface takes the form of a small ovoid mass 

 folded upon itself, and the upper leaf appears to be continuous with the floor of the 



Bin. 



mi 



a. 



CoE 

 anb-l 



FK;. 7. A mesial sagittal section of the pituitary gland (Leptonychotes weddellii). (Semidiagrammatic. ) 



anl.l. Anterior lobe : A A, its front part ; 



15 B, its posterior part (see Plate II.). 

 tnid.l. Intermediate portion. 

 post. I. Posterior lobe. 



n. Neck of the infundibulum. 

 op.l. Optic tract. 



x. Hypothetical mass on the superior aspect of 



the infundibulum. 

 .SIM. Sinusoids. 



col. Colloidal substance formed in the middle lobe. 

 b.v. Large blood-vessels in the posterior lobe (often 



filled with colloid). 



3rd ventricle ; its structure, however, in no way resembles either grey or white 

 matter, being made up of strands of conglomerate cells (syncytium) between which is 

 a considerable amount of connective tissue and some relatively large vessels (text-figs. 

 8 and 9). Below this body comes a layer continuous with the posterior lobe, then 

 the persistent cleft continues with the third ventricle and passing some way into 

 the " neck " of the posterior lobe, and below this again the lower part of the neck in 

 which a small amount of the above atypical tissue also occurs, but, as will be seen, 

 quite separate from the main mass. 



(ROY. SOC. EDIN. TRANS., VOL. XLVIII., 863.) 



