616 



THE NERVOUS SYSTEM. 



occupies the fossa hypophyseos in the floor of the cranium. It is composed of two 

 lobes a large anterior lobe and a smaller posterior lobe, which are closely applied 



the one to the other. The in- 

 f undibulum, which ( extends down- 

 wards from the tuber cinereuni, 

 is attached to the posterior lobe. 



Foramen inter- 



ventriculare 



Anterior 



commissure 



Third ventricle 



Corpus, 

 mamillare 



Optic nerve 

 Infundibulum 



Hypophysis 



The infundibulum and posterior 

 lobe of the hypophysis are developed 

 in the form of a hollow diverticulum, 

 which grows downwards from the 

 floor of that part of the embryonic 

 brain which afterwards forms the 

 third ventricle. The original cavity 

 of this diverticulum becomes ob- 

 literated, except in the superior part 

 of the infundibulum. In structure^ 

 the posterior lobe of the hypophysis 

 shows little trace of its origin from 

 the wall of the brain -tube. It is 

 chiefly composed of connective tissue 

 and blood-vessels, with branched cells 

 scattered throughout it. 



The anterior lobe has quite a 

 different origin, and may be regarded 

 as the functional part of the hypophysis. It is derived from a tubular diverticulum 

 which grows upwards from the primitive buccal cavity or stomodseum. Its connexion 

 with the latter (canalis craniopharyngeus) is in the course of time cut off, and the 

 diverticulum becomes encased within the cranial cavity in intimate association with the 

 cerebral portion of the organ. Structurally, it consists of tubules or alveoli, lined with 

 epithelial cells and surrounded by capillary vessels. Its structure is in some respects 

 not unlike that of the parathyreoid 

 bodies. In the disease known as 

 acromegaly, the hypophysis is usually 

 greatly enlarged. 



FIG. 542. MEDIAN SECTION THROUGH THE HYPOPHYSEAL 



REGION IN A CHILD TWELVE MONTHS OLD. 



(From a photograph by Professor Symington.) 



Foramen inter- 

 ventriculare 



Lamina Terminalis. This is 

 a thin, delicate lamina which may 

 be seen on the basal aspect of the 

 brain, 'stretching from the upper 

 aspect of the optic chiasma in an 

 upward direction to become con- 

 nected with the anterior end of the 

 corpus callosum. 



Anterior Commissure of the 

 Cerebrum. In the anterior part 

 of the cleft between the two 

 thalami, and immediately in front 

 of the columns of the fornix, a 

 round bundle of fibres crosses the 

 median plane. This is the anterior 

 commissure. 



Ventriculus Tertius. The 

 third ventricle is the narrow cleft 

 which separates the two thalami. 

 Its depth rapidly increases from 

 behind forwards, and it may be said to extend from the pineal body behind to tl 

 lamina terminalis in front. Its floor is formed by the tuber cinereum and th 

 corpora mamillaria : the gray matter of the substantia perforata posterior, an 

 the tegmenta of the cerebral peduncles may also be looked upon as forming pai 

 of the floor (Figs. 542 and 543). It is interesting to note that the central gra , 



Anterior commissure 

 Third ventricle 

 Corpus mamillare 



Subarachnoid tissue 

 in cisterna basalis 



Infundibulum 



Hypophysis 



Posterior part of 

 subarachnoid space 



Basilar part of the 

 occipital bone 



Sphenoidal sinus 

 FIG. 543. MEDIAN SECTION THROUGH THE HYPOPHYSEAL 

 REGION IN THE ADULT. 



