192 DISSECTION OF THE BRAIN. 



matter, and numerous vessels penetrate it. This structure forms the 

 hinder part of the floor of the third ventricle. 



The corpora albicantia (corp. mamillaria, e) are two small, white 

 bodies, about the size of peas, which are constructed in greater part by 

 the crura of the fornix. If one, say the right, is cut. across, it will be 

 seen to contain gray matter. In front of them is the gray mass of the 

 tuber cinereum. 



The median eminence of the tuber cinereum (h) forms part of the third 

 ventricle, and is continuous with the gray substance in that cavity. In 

 front of it are the optic tracts and commissure, and from its centre projects 

 the following. 



The infundibulum (funnel) is a conically-shaped tube which reaches 

 from the tuber cinereum to the upper part of the posterior lobe of the 

 pituitary body. It consists of a layer of gray matter, surrounded by the 

 pia mater; and it is lined by the ependyma of the third ventricle, as far 

 as it is pervious. In the foetus this tube is open between the third ven- 

 tricle and the pituitary body, but in the adult it is closed inferiorly. 



The pituitary body will be very imperfectly seen when it has been dis- 

 lodged from its resting-place : therefore it should be sometimes examined 

 in the base of the skull by removing the surrounding bone. Its use is 

 unknown. 



It is situate in the hollow (sella Turcica) on the sphenoid bone, and 

 consists of two lobes, anterior and posterior. The anterior is the largest, 

 and is hollowed out behind, where it receives the round posterior lobe. In 

 the adult this body is solid, and firm in texture ; but in the foetus it is hol- 

 low, and opens into the third ventricle through the infundibulum. 



Structure. It is firm and reddish externally, but softer and yellowish 

 internally. In it are nucleated cells, mixed with a granular semi-fluid 

 substance; and the whole is contained in roundish spaces, which are con- 

 structed by a strorna of areolar tissue with bloodvessels (Sharpey). 



Dissection. To see the lamina cinerea and the anterior termination of 

 the corpus callosum, the hemispheres are to be gently separated from each 

 other at the fore part. 



The lamina cinerea (m) is a thin concave layer of gray substance, 

 which gradually tapers forwards from the tuber cinereum to the anterior 

 termination of the corpus callosum. This stratum closes the anterior part 

 of the third ventricle, and is continuous laterally with the anterior perfo- 

 rated spot. In consequence of its great thinness, this structure is often 

 broken through in removing the brain. 



The corpus callosum (n), bent in front, is continued horizontally back- 

 wards in the longitudinal fissure to the lamina cinerea, and ends in two 

 white narrow bands, the fillets or peduncles of the corpus callosum : each 

 band is continued onwards by the side of the lamina cinerea to the anterior 

 perforated spot. To the anterior bend of the corpus callosum the term 

 knee (genu) is applied, and to the prolonged central part the appellation 

 rostrum has been given. Laterally the corpus callosum reaches into the 

 frontal lobe, and forms part of the floor of the lateral ventricle. 



Anterior perforated spot (substantia perforata antica, /) is a space near 

 the inner end of the fissure of Sylvius, which is situate between the frontal 

 and temporo-sphenoidal lobes of the cerebrum, and external to the optic 

 tract. On the inner side it is. continuous with the lamina cinerea; and 

 crossing it, from within outwards, is the fillet of the corpus callosum. 

 This space is gray on the surface; it corresponds with the corpus striatum 



