FUNCTIONAL ANALYSIS, CENTRAL AND PERIPHERAL 59 



more simply organized, chiefly for co-ordinated mass movements. 

 The sensory zone with its own apparatus of correlation, accordingly, 

 bulks larger than the motor zone. 



Though the peripheral sensory apparatus in Amblystoma differs 

 from the human in many details, yet the general principles of its 

 organization are similar; the structural organization of the central 

 apparatus of adjustment, on the contrary, is so radically different 

 that comparisons are difficult. Here the several functional systems of 

 peripheral nerve fibers enter the brain in fascicles of the nerve roots, 

 which are physiologically as specific as are those of mammals ; but at 

 the first synapse this specificity may almost completely disappear, in 

 so far as it has visible structural expression. The root fibers of all 

 sensory systems (except, perhaps, the olfactory) terminate by wide 

 arborizations in a few common fields of neuropil, in each of which 

 several of these systems are inextricably mingled. This neuropil is a 

 common synaptic pool for all entering systems. The several pools are 

 interconnected with one another and with similar pools in other 

 parts of the brain stem, and there is no supreme cortical regulator. 

 The translation of sensory experience into adaptive behavior and the 

 integration of this behavior are somehow accomplished within this 

 interplay of the local activities of the brain stem. 



The sensory zone is continuous from the dorsal gray colunm of the 

 spinal cord to the olfactory field, comprising the dorsolateral part of 

 the medulla oblongata, the auricle in the cerebellar region, the an- 

 terior medullary velum and a small amount of contiguous tissue, the 

 tectum of the midbrain, pretectal nucleus, dorsal thalamus, olfactory 

 bulb with the adjoining anterior olfactory nucleus, and optionally the 

 septum and some other parts of the hemisphere, a portion of the 

 hypothalamus, and the ventrolateral neuropil of the peduncle. The 

 fields optionally included receive terminals of the nervus terminalis 

 (p. 267); the hypothalamus has a small but significant connection 

 with the optic nerve, the basal root of which also connects with the 

 peduncle. In some vertebrates the epithalamus receives fibers from 

 the parietal eye, but in Amblystoma these have not been seen, and in 

 this animal the predominant functions of the "optional" areas are of 

 intermediate-zone type. The body of the cerebellum and the pallial 

 part of the cerebral hemisphere might be assigned to the sensory zone 

 as here defined anatomically; yet, as previously mentioned, they are 

 excluded from this zone because of their distinctive physiological 

 characteristics and their remarkable specialization in higher animals. 



