590 General Symptomatology of Diseases of the Brain. 



the ungulates the pyiaiuidal tract is very poorly developed and can be traced as far 

 as the 4th cervical vertebra only (Dexler and Margulies). In the carnivora the 

 tract is more fully developed and can be traced as far as the sacrum, but it is less 

 distinct than in man. 



In birds there are no direct motor tracts connecting the brain and spinal cord, 

 the whole central motor path being in connection with the subcortical centers. It 

 is only in the parrot that a nerve path comparable to the pyramidal tract occurs 

 (v. Kalischer). 



The cells from which the peripheral motor paths arise a»e collected into 

 groups of varying size, having a common function, and forming numerous reflex 

 centers both in the brain and spinal cord, stimulation setting in action one or more 

 muscles, or under certain circumstances, whole groups of muscles on one or both 

 sides of the body in definite sequence. The complex reflex mechanisms which permit 

 the correlation of movements of certain parts of the body with movements of other 

 parts, such as running, walking, etc., are controlled by the subcortical centers. With 

 development the subcortical centers encroaches upon the sphere of action of the 

 cortex, liut apart from this other exactly similar movement can be carried out with- 

 out calling into play the reflex mechanism, the brain cortex taking part in numerous 

 reflex mechanisms to the exclusion of the subcortical centers. This is rendered 

 possible by the pyramidal tract which in the ungulates controls the head and neck, 

 and in carmvora the limbs also. The lower the position occupied by an animal in 

 the scale of development the greater the independence of the individual elements 

 of the motor paths on the opposite sides. 



From the foregoing it is clear that the pyramidal and the extrapyramidal 

 tracts can convey the socalled voluntary impulses of the cortex and be effective on 

 both sides of the body. As all these j^aths and centers are disposed over a wide 

 area of brain, and as the subcortical centers are somewhat independent of the cortex, 

 lesions capable of causing total central paralysis in animals must be very extensive 

 and more so than those producing the same effect in man. 



In the coordination and regulation of movements several portions of the 

 nervous system take part (see fig. 79). 



Two principal portions control coordination and regulation; the sensory paths 

 which inform the cells of the central nervous system regarding the individual nmscle 

 functions, the position of the whole or of some part of the body, and the motor 

 paths which convey stimuli to the muscles depending upon the most varied sensory 

 impressions in the nerve cells. The component parts of the centripetal path are 

 not all of equal value as regards coordination. In certain muscular functions the 

 special sensory paths are involved, in others the vestibular or the optic paths; in 

 the equilibration of the whole or of parts of the body the paths leading to the 

 cerebellum or even the cerebellum itself may be concerned. Each part of the co- 

 ordinating system is functional up to a certain point. As the various components 

 are not of exactly equal value they are able, so to speak, to hand over the excess 

 to the opposite side. This is particularly the case with regard to the organ of 

 vision and consequently there is more or less ataxia of the eyes. 



By means of the coordinating mechanism the body is in a position to carry 

 out each muscular function with ease and certainty and with the least possible waste 

 of energy. 



The extent and severity of the paralysis depends upon the 

 portion of the intracranial motor path injured and the extent of 

 the injury. As the central motor path covers a somewhat large 

 area at its origin and local lesions of the brain tend to remain 

 limited in extent either permanently or for some length of time, 

 the paralysis is limited in cases of disease of the motor areas 

 and owing to the decussation of the fibers the sjanptoms are ex- 

 hibited by the other side of the body. The paralysis tends to be 

 monoplegic in type, affecting either one side of the face or one 

 limb. The paralysis is generally incomplete and only a more 

 or less pronounced paresis is observed. If several centers are 

 involved in the morbid processes there may be injury to motor 

 areas on both sides, causing asymmetrical monoplegia. Fur- 

 ther, it is to be observed that in cortical injuries the paralysis 



