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HAROLD J. COOPER 



A. GROSS FEATURES 



The general topography of the ground-squirrel hypophysis is 

 very similar to that of other mammals (figs. 1 and 2). Using 

 Tilney's terminology, it has a pars buccalis (PG), derived from 

 the ectoderm of the buccal cavity (but possibly also including a 

 portion from the pharyngeal entoderm), and a pars neuralis 

 (PA/), derived from the nervous system. These two portions lie 



Fig. 1 Midsagittal section through the ground-squirrel hypophysis (semi- 

 diagrammatic). B, brain; 3rdV, third ventricle; SB, sphenoid bone; PN, pars 

 neuralis; RL, residual lumen; PI, PI 1 , PP, pars infundibularis; PG, pars distalis; 

 I, infundibulum; IC, infundibular cavity; D, dura; OC, optic chiasma; PT, pars 

 tuberalis. X 25. 



in contact. The original cavity of the pars buccalis (residual 

 lumen (RL)) is maintained in the adult form, and serves to sep- 

 arate the pars buccalis into two divisions, structurally, and 

 probably also functionally distinct, namely, the pars juxta- 

 neuralis (PI, PI 1 , PI 2 , PT), and the pars distalis. The pars 

 juxtaneuralis is divided into a pars infundibularis (PI, PI 1 , PI 2 ), 

 investing the infundibulum and infundibular process, and a pars 

 tuberalis (PT), extending over the tuber cinereum. Since the 



