All Analysis of the Juxta-Neural Epithelial Portion etc. 259 



third ventricle, and the part of the gland in relation with them may 

 therefore be termed the juxta-neiiral epithelial portion of the hypo- 

 physis. The intimacy of the relation between these parts depends 

 upon their juxtaposition, and also upon the fact that the neural and 

 glandular tissues are connected with each other by means of nerve 

 fibers. Although the nature of this connection deserves more extended 

 study than it has yet received, this phase of the question will not 

 be considered here. 



The object of this paper is to present an analysis of the juxta- 

 neural epithelial portion, and to call attention to a hitherto undescribed 

 part of the gland. The ontogenesis of this latter part has been 

 followed through a number of embryonic and fetal stages in the cat 

 and common fowl and it is now possible to give a complete account 

 of its development as well as that of the entire juxta-neural portion 

 of the pituitary gland in these two forms. 



The hj^pophysis is usually described as made up of two lobes, 

 an anterior or glandular lobe and a posterior or neural lobe. This 

 description is open to serious objection, first because the posterior lobe 

 is seldom exclusively neural and second because the so-called neural 

 lobe is situated superiorly in many species, 'and in some instances 

 occupies an anterior position. To obviate some of these difficulties 

 it has recently been suggested that the neural lobe be termed the 

 pars nervosa, the glandular tissue surrounding it the pars intermedia 

 and the remainder of the gland tissue the pars glandularis. But, for 

 the exact purposes of comparative study, it is advantageous, in so far 

 as possible, to analyze a given structure on the basis of its onto- 

 genesis. No organ more readily lends itself to such an analysis than 

 the hypophysis. 



The neural ectoderm in the basal region of the diencephalon 

 gives rise to a ventral evagination. The oral ectoderm with, perhaps, 

 some elements from the entoderm of the foregut, gives rise to a 

 dorsal evagination. These two evaginations meet and fuse. Sub- 

 sequently the body so formed becomes completely intra- cranial. The 

 connection with the brain is retained, that with the mouth cavity is 



lost. This description holds good for the majority of forms which 



17* 



