848 



THE NERVOUS SYSTEM 



the brain. The front portion of this wall is the lamina terminalis and in the ven- 

 tricular side of the upper part of this lamina the anterior commissure of the 

 cerebrum is apparent. 



The optic chiasma lies across and presses into the lower portion of the lamina 

 terminalis, and in so doing produces an anterior recess in the cavity of the ventri- 

 cle known as the optic recess. Behind the optic chiasma the floor of the third 

 ventricle bulges slightly, giving the outward appearance known as the tuber 

 cinereum, and the cavity bounded by this terminates in the infundibular recess. 



The tuber cinereum then is a hollow, conical projection of the floor of the 

 third ventricle, between the corpora mammillaria and the optic chiasma. Its wall 

 is continuous anteriorly with the lamina terminalis and laterally with the anterior 

 perforated substance. 



The infundibulum is but the attenuated apex of the conical tuber cinereum, 

 and forms the neck connecting it with the hypophysis. It is so drawn out that it 

 is referred to as the stalk of the hypophysis. The cavity of the tuber cinereum 

 (infundibular recess) is sometimes maintained throughout the greater part of the 

 length of the infundibulum, giving it the form of a long-necked funnel. Near the 

 hypophysis the cavity is always occluded. 



Fig. 669. — Diagrams of the Hypophysis Cerebri. (After Testut.) 

 A, posterior surface; B. transverse section; C, sagittal section; 1, anterior lobe; 2, posterior 

 lobe; 3, infundibulum; 4, optic chiasma; 5, infundibular recess; 6, optic recess. In C the 

 infundibulum is relatively much shorter than in the actual specimen. 



The hypophysis cerebri (pituitary body or gland) is an ovoid mass terminating 

 the infundibulum. It lies in the sella turcica of the sphenoid bone, where it is held 

 down and roofed in by the diaphragma sellce, a spheroid pocket of the dura mater. 

 It consists of two lobes, a large anterior lobe, the glandular or buccal lobe, and a 

 smaller posterior or cerebral lobe. The posterior lobe is usually enclasped in a 

 concavity of the anterior lobe. 



Development. — The posterior or cerebral lobe alone is originally continuous with and a part 

 of the infundibulum. It alone represents the termination of the hoUow diverticulum which, 

 in the embryo, grows downward from that part of the anterior cerebraLvesiclewhj later 



become s the tliird ventriflo. The original cavity afterward becomes obliterated except in the 



^/^ upperpart of th(^ infundibulum. It is, therefore, of cerebral origin. The anterior or buccal 



lobe arises quite differently. It is developed from an upward tubular diverticulum (Rathke's 

 pouch) of the primitive buccal cavity. In the higher vertebrates, including man, its connection 

 with the buccal cavity becomes obliterated as the cartilaginous base of the cranium is consoh- 

 dated, but in the myxinoid fishes the connection remains patent in the adult. Cut of? within 

 the cranial cavity, the embryonic buccal lobe assumes its intimate association with the cerebral 

 lobe. In a})out the second month of fetal life it begins to develop numerous secondary diverti- 

 cula whieh become the epithelial structures evident in tlie adult lumian subject. 



Structure. — The posterior or cerebral lobe retains no organized structure. It may be said 

 to consist of a mass of neuroglia and other fibrous connective tissue with the cells belonging to 

 these and a moderate supply of blood-vessels, with some sympatlietic cell-bodies and fibres for 

 the blood-vessels. The anterior or glandular lobe is probably the functional part of the organ. 

 In addition to its abundant supporting tissue, it consists of compartments lined with two kinds of 

 cuboidal cells — cells of diiTerent size and different staining properties. The principal or more 

 numerous cells are smaller, with thickly granular cytoplasm. In mixtures containing orange G 

 and fuchsin tliesc cells stain orange, while the chnmiophilc cells, the larger and less numerous 

 variety, take the fuchsin deejjly. The compartments have an abundant blood supply. Near 

 the interlobar sejjtuni, the cells frequently are arranged to form small vesicles ^which contain 

 colloid substance, reseml)ling the typical structure of the thyreoid body. 



Like the epiphysis, the hypophysis must be regarded as glandular — a gland with internal 

 secretion. In the case of giants and in acromegaly it is usually greatly enlarged. The principal 

 cells increase greatly in number after removal of the thyreoid body. 



The fundaments of the optic nerve are derived from this portion of the telen- 

 cephalon, though the nuclei of termination of its fibres are located in the thalam- 



