828 THE NERVOUS SYSTEM 



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 re- 

 ferred to as the stalk of the hypophysis. The cavity of the tuber cinereum (in- 

 fundibular 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 hypo- 

 physis the cavity is always occluded. 



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 selliK, a circular fold 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 enclasped in a concavity of the an- 

 terior 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 hollow diverticulum which, 

 in the embryo, grows downwards from that part of the anterior cerebral vesicle which later 

 becomes the third ventricle. The original cavity afterwards becomes obliterated except in the 

 upper part of the 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 consolidated, 

 but in the myxinoid fishes the connection remains patent in the adult. Cut off within the 

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

 lobe. In about the second month of fetal life it begins to develop numerous secondary diverticula 

 which become the epithelial compartments evident in the adult human subject. 



FIG. 617. 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. 



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 



_, , 1 deeply. The compartments have an 



abundant blood supply. 



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 optic nerve is derived from this portion of the telencephalon, though the 

 nuclei of termination of its fibres are chiefly in the thalamencephalon and mesen- 

 cephalon. The optic apparatus consists of the retinsp and optic nerves, the optic 

 chiasma, the optic tracts, the superior quadrigeminate bodies with their connections 

 with the nuclei of the eye-moving nerves, the metathalamus, the pulvinar of the 

 thalamus, and the visual area of the occipital lobe of the cerebral cortex. The 

 fibres of the optic nerves arise from the cells of the ganglion-cell layer of the retinae. 

 The fibres which arise in the mesial or nasal halves of each retina cross the mid- 

 line to find their nuclei of termination in the central grey substance of the opposite 

 side, while those from the outer or lateral halves terminate on the same side. 



The optic chiasma (optic commissure) is functionally independent of the struc- 

 tures of the optic portion of the hypotlmlamus adjacent to it. It is formed by the 

 approach and fusion of the two optic nerves, and is knit together by the decussating 



