Litt le is known of the development, connections, and functions of the claustrum. Available data is ext remely contradictory (Grinshtein, Filimonov, 1966; Crosby et a l . , 1962). There are isolated accounts o f co r t i c a lp ro j ec t i onson thec l aus t rumf romdi f f e r en t cytoarchitectonic zones of the ce rebra l cortex, shown by Marchi ' s method (Hirasawa et a l . , 1938; Kato, 1938; Berke, 1960) and Nauta's method (Whitlock and Nauta, 1956; Hirata, 1965). However, these accounts mere ly state that d i rec t cor t i co-c lans t ra l connections exist without descr ibing thei r spatial organization. Carman et a l . , (1964) found some evidence of topographical organization of var ious brain regions within the rabb i t ' s c laustrum. Druga (1966, 1968) using Nauta's method on cats, obtained much new information and descr ibed in detail the course of nerve f ibers from various cytoarchitectonic a reas of the cortex to the claustrum and the topographic organization of the project ions in i ts an teropos ter ior and mediolateral dimensions. Connections between a reas of the cortex with known functions and the claustrum is st i l l an unsolved problem. More information on this subject is needed before a morphological classif icat ion of the descending connections could be made on a functional basis . Much attention is now being paid to mechanisms for centrifugal regulation of the afferent flow of information. This consideration is needed for an understanding of integrative processes in the central nervous system (Meshcherskii , 1967; Ochs, 1969). The work of Rasmussen (1964), Katsuki (1966) and Gershuni et al., (1967) has shown that centrifugal effects within the auditory analyzer system exert a definite regulatory influence on the propagation on the centr ipetal impulses ascending specific auditory pathways. The p a r t i cipation of the c laustrum in pitch discr iminat ion (Choraznya et a l . , 1965), and activation of its an ter ior par t s via specific auditory pathways (Hassamannova et a l . , 1967) have also been demonstrated. Segundo and Machne (1956) have shown that the c laustrum receives tactile, nociceptive, proprioceptive, v iscera l , olfactory, andvest ibular information without summation or general izat ion. Spector (1969)has concluded that functional heterotopic and he terosensory convergence occurs in the claustrum, but that uniformity of responses does not~ He postulates that somatic and auditory impulses reach the c l aus t r av ia the corresponding specific thalamic re lay nuclei. From this perspect ive it is important to study the organization of the descending connections of the auditory and vest ibular cortex to the claustrum from two points of view: the s t ructure of the corticofugal pathways from areas with specific functions, and the possible effect of impulses t ransmit ted along them on the analysis of auditory and vest ibular information in the claustrum.