NERVOUS CENTRES. (HUMAN ANATOMY. THE ENCEPHALON.) 703 



radiate extensively. It may be stated to con- 

 nect the convolutions of the middle lobes and 

 the corpora striata. 



3. The posterior commissure is a band of 

 fibres, extended between the posterior extre- 

 mities of the optic thalami, upon which rests 

 the base of the pineal body. Those fibres, 

 which immediately support that body, have 

 been distinguished as the pineal commissure; 

 but as they are evidently part of the same 

 system as those which constitute the posterior 

 commissure, there seems no good reason for 

 separating them. 



4. The soft commissure is also extended be- 

 tween the thalami. It is composed of vesi- 

 cular matter with fibres, which pass from 

 one side to the other. The intermixture 

 of its fibres with vesicular matter distin- 

 guishes it from the other transverse commis- 

 sures already described. A layer of a simi- 

 lar nature connects the locus niger of each 

 crus cerebri, and fills up the space between 

 the crura interpeditncular space. This has 

 been already described as the pans Tarini, 

 posterior perforated space. It consists of 

 fibrous matter intermixed with vesicular, ex- 

 tended between the crura cerebri. It seems 

 analogous to the soft commissure, and there- 

 fore entitled to be regarded as a commissure. 



Of the manner in which the commissures 

 connect the various parts between which they 

 are placed, it is difficult to form an exact 

 opinion. It is most probable that they form 

 an intimate union with the grey matter of the 

 segments which they serve to connect. It 

 might also be conjectured that they are conti- 

 nuous with some of the fibres of the segments 

 which they unite, or that they interlace with 

 them in some intricate way, so as to come into 

 intimate or frequent contact with them. 



Tuber cinereum. At the base of the brain 

 we have already described a layer of pale grey 

 matter which fills up the interval between the 

 mamillary bodies and the optic commissure. 

 It extends above the optic commissure for- 

 wards to the anterior reflexion of the corpus 

 callosum, and forms intimate connections with 

 the anterior pillars of the fornix, the optic 

 tracts, the septum lucidum, and at the floor 

 of the third ventricle with the optic thalami. 

 It consists of vesicular matter with fibres, and 

 resembles very much the soft commissure, to 

 which it is very probably analogous in office. 



The process called infundibulum or pituitary 

 process extends from the inferior surface of the 

 tuber cinereum down to the pituitary body. 

 It is hollow, wide above, where it commu- 

 nicates with the third ventricle, and narrow 

 below at the pituitary body. When cut across, 

 fluid will escape from the third ventricle 

 through it, and a probe passes readily from 

 that cavity into it. It is composed of a layer 

 of granules, derived, no doubt, from the epi- 

 thelial lining of the third ventricle, and some 

 vesicular matter with bloodvessels and fibrous 

 tissue, which latter is derived from the pia 

 mater, and the special sheath of arachnoid 

 reflected upon it. 



Pituitary body. The process just described 

 is the connecting link between the brain and 

 that glandiform body, the pituitary gla?td or 

 hypophysis. This body, situate in the sella 

 Turcica, is of a rounded form, longer in the 

 transverse than the aritero-posterior direction, 

 concave on its superior surface, into which the 

 pituitary process is inserted. It is surrounded 

 by dura mater, which projects over it, leaving 

 an opening for the passage of the infundi- 

 bulum. 



The pituitary body is about six lines in its 

 transverse diameter and three lines from before 

 backwards: its weight, including the infundi- 

 bulum, is about eight grains. It consists of 

 two lobes, one anterior, the other posterior. 

 The former is kidney-shaped and lodges the 

 latter in the notch of its posterior edge. In 

 point of size the anterior lobe is nearly double 

 the posterior. 



The colour of the posterior lobe is lighter 

 than that of the anterior, and resembles that of 

 the grey matter of the brain. 



This body is proportionally larger in early 

 life than at the later periods, and it is certainly 

 more developed in the lower mammalia than 

 in man. It is very large in fishes, and pro- 

 bably reaches its maximum of size in that class 

 of animals. 



The structure of the pituitary body resem- 

 bles very much the grey cerebral matter. It is 

 composed of large nucleated vesicles, sur- 

 rounded by a granular matrix, with bundles of 

 white fibrous tissue. This fibrous tissue either 

 forms an essential element in its constitution, 

 or accompanies the bloodvessels which are 

 found in it in great numbers. Its substance is 

 soft, but not so soft as the cerebral matter, 

 and when pressed between the fingers is re- 

 duced to a greyish pulp, like the substance of 

 an absorbent gland in an early stage of suppu- 

 ration. 



Earthy concretions have been occasionally 

 but very rarely found in the pituitary body. 

 This circumstance, its colour, its glandiform 

 character, and its extra-cerebral situation in 

 connexion with the third ventricle, give it a 

 certain degree of analogy to the pineal body. 

 Jiut in this latter nervous fibres have been 

 found, of which I have failed to discover any 

 trace in the pituitary, nor is the pituitary body 

 connected to the brain by fasciculi of fibres as 

 the pineal body is. The use of both is equally 

 involved in obscurity ; but from their con- 

 stancy it may be argued that their function is 

 not unimportant. It has been supposed that 

 the pituitary body is a large ganglion belong- 

 ing to the sympathetic system : this opinion, 

 however, wants the all-important foundation of 

 anatomy to rest upon, inasmuch as we find 

 that the body in question is devoid of the ana- 

 tomical characters of a ganglion. It may with 

 more propriety be classed with the glands 

 without efferent ducts; and from its numerous 

 vessels, and its close relation to part of the 

 venous system within the cranium, it may be 

 connected with the process of absorption or re- 

 moval of the effete particles of the brain. 



