RELATION BETWEEN STRUCTURE AND FUNCTION. 17 



blood. So also in the case of the individual spinal nerve- 

 cells, innervating a particular muscle, we suppose, that 

 their co-ordinate action and synchronous discharge depends 

 rather on some physiological quality common to all which 

 cannot be accorded to them by mere spatial arrangement. 



A question that obviously presses for answer, is whether 

 when a muscle contracts either renexly or voluntarily, all 

 the parts of it innervated from all the spinal roots con- 

 tract together, or whether some parts of it contract for 

 some movements, and others for other movements, and 

 so on, and so whether the segmentally different parts of 

 the muscle are used severally for different functional 

 actions In reflex movements, and in movements evoked 

 from the cortex of the brain, we can say that the discharge 

 of motor impulses to a pluri-segmental muscle of the fore- 

 arm, or wrist, or hand, is always pluri-segmental, and 

 involves the whole length of the serial group of intra-spinal 

 nerve-cells which innervates the muscle extending through 

 its full number of segments of the cord. The afferent and 

 cerebral channels of the cord treat the pluri-segmental 

 motor stations or nuclei of these limb muscles as entities 

 of homogeneous structure, as in fact, physiological units. 



This serves to emphasise the physiological homogeneity 

 of limb-muscle and nerve-trunk, and the physiological 

 heterogeneity, in spite of morphological unity, of the 

 spinal nerves-root in the limb-region of the body. 

 The spinal nerve-roots of the thoracic region are, 

 from the physiological point of view, less heterogeneous. 

 The peripheral nerve-trunk is the physiological collection 

 of nerve-fibres, e.g., flexors collected together, vaso- 

 dilators, included with motors to muscles, &c. The nerve- 

 root is the morphological collection, it contains com- 

 mingled into one such heterogeneities as adductors of the 

 hallux with protrusor pelvic muscles. 



