CENTRAL AUTONOMIC MECHANISMS 



963 



the regulation of autonomic actixities. To a large 

 extent this is true, but he sometimes forgets that this 

 region is a part of a much more extensive system of 

 neurological circuits. It is true that here we have a 

 condensation of fibers of passage con\"e\ ing impulses 

 from higher and lower regions and that here are 

 'integrated' many converging influences, so that the 

 product conforms to a pattern suitable for the needs 

 of the organism. These neural patterns may be reinte- 

 grated at a lower level of the brain stem and their 

 effects are eveniualK- consummated b\' the spinal 

 cord complexes. 



Anatomy of Hyjiothalamui 



It is perhaps suitable to summarize briefly the 

 structure, relationships and connections of this region 

 as they are understood today (84, 85). Some of these 

 structures are shown in figure 2 of CUiapter LXIII of 

 this work devoted to neurological mechanisms in 

 emotion. Mitchell (121) remarks, '". . . anyone who 

 suffers from the delusion that anatomy is an effete 

 subject with no problems left to solve is advised to 

 read even a tithe of the bewildering conglomeration of 

 literature on the hypothalamus and its connections. 

 If he does delusion will be replaced by disillusion." As 

 this region has become more accessible through the 

 use of modern technicological developments, it is 

 possible increasingly to fit in its activities with tho.se 

 of other parts of the central nervous system. VVe can 

 also take a more disinterested view of its nuclear con- 

 figuration because, while this region contains a num- 

 ber of well-defined morphologically distinguishable 

 groups of neurons, embedded in a background of 

 nerve fibers and diffusely scattered neurons, only two 

 or three of these cell groups may be related to any 

 specific function. As a matter of fact, areas of the 

 hypothalamus seem to be more important than nuclei. 

 However, since some nuclei do have definite functional 

 relationships and since their designation is important 

 from the standpoint of orientation, providing a means 

 of communication between the experimentalists, and 

 because in the future this nuclear classification may 

 become of unforeseen importance, a brief description 

 of the hypothalamus is herewith included. 



SUBDIVISIONS OF HYPOTHAL.AMUS AND THEIR NUCLEI. 



The hypothalamus is bounded anteriorly by the 

 lamina terminalis which of course includes the 

 anterior commissure. Here is located the preoptic 

 region, providing a zone of transition between the 

 subcallosal septal region and the hypothalamus. The 

 posterior boundary coincides with the interpedimcular 



fossa. Dorsally we have the h\pothalamic sulcus mark- 

 ing the boundary between hypothalamus and thala- 

 mus. Inferiorly we have the optic chiasma and behind 

 it, the floor of the third ventricle which includes the 

 infundibular stem. The two halves of the area are of 

 course separated by the ventral extension of the third 

 ventricle. The hypothalamus caudal to the preoptic 

 area seems logically di\ided into supraoptic, tuberal 

 and mammillary regions, each of which contains 

 several nuclei. 



a) In tlie supraoptic area, the anterior hypothalamic 

 nucleus is well-defined in some forms but more vague 

 in man in whom it is simply an area dorsal to the 

 optic chiasma. Embedded in it just above the chiasma 

 at the edges of the supraoptic recess is the supra- 

 chiasmatic nucleus. The paraventricular nucleus is a 

 triangular group of darkly staining cells gathered 

 along the sides of the ventricle and extending some- 

 what laterally at its dorsal extremity. The other 

 conspicuous group in this region is the supraoptic 

 nucleus which overlies the beginning of the optic tract 

 and extends a short distance posteriorly from it in the 

 direction of the infundibular stem. This also contains 

 large dark-staining neurons, and these as well as 

 those of the paraventricular nucleus have certain 

 cytological characteristics which indicate that they 

 may be capable of secretory activity. 



b) The second region is the tuberal portion of the 

 hypothalamus. This may be divided into a medial 

 and a lateral region. The lateral area is marked by 

 its heavy content of nerve fibers, both myelinated 

 and unmyelinated, many of which pass through the 

 hypothalamus in a rostrocaudal direction. These 

 fibers constitute the medial forebrain bundle, much 

 of which arises in the olfactory regions farther for- 

 ward and which runs back into the tegmentum of the 

 midbrain. It also contains fibers from the hypothala- 

 mus which descend and contributes, in its turn, con- 

 nections to the hypothalamic neurons. Through much 

 of the extent of this nucleus there are small undiffer- 

 entiated neurons; but, especially in the more caudal 

 reaches, a large number of large dark-staining cells 

 are found, rather irregularl)- grouped. These are 

 especially conspicuous in man and may be important 

 as contributing fibers to the descending connections 

 of the region. Other groups of small neurons, known 

 as the lateral nuclei of the tuber, occur in man but are 

 found only with difficulty in lower forms. The separa- 

 tion between the lateral and the medial areas of the 

 tuberal region is marked by the descending column 

 of the fornix, around which the neurons compressed 

 by its passage have sometimes been called the peri- 

 fornical nucleus. Actuallv, perifornical area would be 



