SECRETION. 459 



the posterior lobe. (Fig. 213) The anterior lobe is developed from an in- 

 vagination of the ectoderm of the buccal cavity and consists of gland tissue 

 surrounded by a thin envelope of connective tissue. It becomes separated from 

 the mouth by the fusion of the sphenoid cartilages. The posterior lobe is an 

 outgrowth from the mid-brain and is connected with the infundibulum of 

 the third ventricle by a short stalk. In the early stages of its development 

 it presents a central cavity which is, however, soon obliterated by the growth 

 of special tissues. It persists in the cat. It has been 

 suggested that the term hypophysis cerebri be reserved 

 for the anterior lobe and the term infundibular body 

 for the posterior lobe. This distinction appears to be 

 desirable inasmuch as in their origin, structure and func- 

 tions they are separate and distinct bodies. 



Histology of the Pituitary Body. If a mesial 

 sagittal section be made through the pituitary it will 

 present an appearance which in a general way is the 

 same in many animals though the details vary some- SECTION "I' 

 what in each animal. In the monkey the arrangement ITARY BODY AND INFUN- 



of the anatomic parts (Fig. 214) is similar to the ar- DIBULUM WITH ADJOIN- 



T, \n ? , 7 , , . ING PART OF THIRD VEN- 



rangement in man. It will be observed that the posterior TR I CL E. a. Anterior 



lobe is solid and that there is no open connection with lobe. a'. A projection 

 the cavity of the third ventricle; that it is invested, over oT^eS^fundlbulumT 

 a large part of its surface, by a thin layer of epithelium. Posterior lobe connected 

 The anterior lobe, which lies in front of it is separated b y a stalk ih the in - 

 by a cleft which is the remnant of the cavity of the f ^ c c tasm.- 

 buccal pouch. Though the appearance of the ante- (Schwaibefrom Quain.) 

 rior lobe, and the epithelial investment of the posterior 

 lobe is somewhat different, the latter is but a differentiation of the former, a 

 procedure that takes place in fetal life. The epithelial investment is 

 usually spoken of as the pars intermedia, and regarded histologically and 

 physiologically as a part of the posterior lobe. Superiorly the anterior lobe 

 and the pars intermedia are united, though a portion of the latter passes 

 upward and embraces, if it does not entirely surround, the infundibular 

 stalk; inferiorly and posteriorly the two bodies also unite. The posterior 

 surface of the posterior lobe is free from epithelial investment in the mid-line. 

 The extent to which the epithelium invests the posterior lobe varies in dif- 

 ferent animals. In the cat and dog it is almost complete. 



Microscopic examination of the anterior lobe shows the presence of 

 granular epithelial cells, the descendents of the original buccal epithelium, 

 arranged in columns between which pass large thin-walled blood-vessels. 

 In view of the physiologic importance of this lobe it is believed that the 

 granules of the cell represent an internal secretion, which passes into the 

 blood-stream and is thus distributed to various regions of the body. 



The pars intermedia consists of several layers of finely granular epithelial 

 cells which develop a colloid material that subsequently passes into the pos- 

 terior lobe where it becomes hyaline in character. The epithelial investment 

 is separated from the posterior lobe by a layer of blood-vessels though 

 columns of cells penetrate it. 



The posterior lobe consists of neuroglia cells and fibers. True nerve- 



