

THE CHROMAPHIL AND CORTICAL SYSTEMS . 1277 



terior lobe : the former is derived from the ectoderm of the stomodeum, the latter 

 from the floor of the fore-brain. About the fourth week there appears a pouch- 

 like diverticulum of the ectodermal lining of the roof of the stomodeum. This 

 diverticuluin, pouch of Rathke (Fig. 1182), is the rudiment of the anterior lobe of 

 the hypophysis; it extends upward in front of the cephalic end of the notochord 

 and the remnant of the buccopharyngeal membrane, and comes into contact wuh 

 the under surface of the fore-brain. It is then constricted off to form a closed 

 vesicle, but remains for a time connected to the ectoderm of the stomodeum by a 

 solid cord of cells. Masses of epithelial cells form on either side and in the front 

 wall of the vesicle, and by the growth between these of a stroma from the mesoderm 

 the development of the anterior lobe is completed. The upwardly directed hypo- 

 physeal involution becomes applied to the antero-lateral aspect of a downwardly 

 directed diverticulum from the base of the fore-brain (page 744). This divertic- 

 ulum constitutes the future infundibulum in the floor of the third ventricle 

 while its inferior extremity becomes modified to form the posterior lobe of the 

 hypophysis. In some of the lower animals the posterior lobe contains nerve cells 

 and nerve fibers, but in man and the higher vertebrates these are replaced by 

 connective tissue. A canal, craniopharyngeal canal, is sometimes found extending 

 from the anterior part of the fossa hypophyseos of the sphenoid bone to the under 

 surface of the skull, and marks the original position of Rathke's pouch; while at 

 the junction of the septum of the nose with the palate traces of the stomodeal 

 end are occasionally present (Frazer). 



THE PINEAL BODY. 



, The pineal body (epiphysis} is a small reddish-gray body, about 8 mm. in length 

 which lies in the depression between the superior colliculi. It is attached to the 

 roof of the third ventricle near its junction with the mid-brain. It develops as an 

 outgrowth from the third ventricle of the brain. 



In early life it has a glandular structure which reaches its greatest development 

 at about the seventh year. Later, especially after puberty, the glandular tissue 

 gradually disappears and is replaced by connective tissue. 



Structure. The pineal body is destitute of nervous substance, and consists of follicles lined 

 by epithelium and enveloped by connective tissue. These follicles contain a variable quantity 

 of gritty material, composed of phosphate and carbonate of calcium, phosphate of magnesium 

 and ammonia, and a little animal matter. 



It contains a substance which if injected intravenously causes fall of blood-pressure. It seems 

 probable that the gland furnishes an internal secretion in children that inhibits the development 

 of the reproductive glands since the invasion of the gland in children, by pathological growths 

 which practically destroy the glandular tissue, results in accelerated development of the sexual 

 organs, increased growth of the skeleton and precocious mentality. 



THE CHROMAPHIL AND CORTICAL SYSTEMS. 



Chromaphil or chromaffm cells, so-called because they stain yellow or brownish with 

 chromium salts, are associated with the ganglia of the sympathetic nervous system. 



Development. They arise in common with the sympathetic cells from the neural 

 crest, and are therefore ectodermal in origin. The chromaphil and sympathetic 

 cells are indistinguishable from one another at the time of their migration from the 

 spinal ganglia to the regions occupied in the adult. Differentiation of chromaphil 

 cells begins in embryos about 18 mm. in length but is not complete until about 

 birth. The chromaphiloblasts increase in size more than the sympathoblasts and 

 stain less intensely with ordinary dyes. Later the chrome reaction develops. The 

 aortic bodies differentiate first and are prominent in 20 mm. embryos. The para- 

 ganglia of the sympathetic plexuses differentiate next and last of all the para- 

 ganglia of the sympathetic trunk. The carotid body is completely differentiated 



