Henry Gray (18251861). Anatomy of the Human Body. 1918.
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 pouchlike diverticulum of the ectodermal lining of the roof of the stomodeum. This diverticulum, 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 with 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 hypophyseal involution becomes applied to the antero-lateral aspect of a downwardly directed diverticulum from the base of the fore-brain (page 744). This diverticulum 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 Rathkes pouch; while at the junction of the septum of the nose with the palate traces of the stomodeal end are occasionally present (Frazer).
4e. 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.
1F. The Chromaphil and Cortical Systems
Chromaphil or chromaffin 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 paraganglia of the sympathetic plexuses differentiate next and last of all the paraganglia of the sympathetic trunk. The carotid body is completely differentiated