478 A MANUAL OF VETERINARY PHYSIOLOGY 



The Optic Thalamus, as we have previously seen (p. 471), is 

 the junction for all afferent impressions prior to distribution to 

 their destination ; it is the main sensory relay station to the 

 cortex. It is considered to be the seat of painful impressions, 

 for lesions of it are associated with acute pain on the opposite 

 side of the body. Its structure suggests that it is also con- 

 nected with motor functions, for destruction of portions of the 

 cortical area leads to degeneration of their corresponding nuclei 

 in the optic thalamus. Connected with the thalamus is the 

 red nucleus, which gives origin to an important spinal motor 

 path in the lower animals (see p. 466). It is supposed that the 

 thalamus is associated with reflex mimetic movements of gesture, 

 physiognomical expression, and of primitive vocalisation. In 

 lesions of the thalamus emotional expressional movements of 

 the human face are lost. Some observers have considered that 

 secretory, vasomotor, and other fibres connected with the sym- 

 pathetic system, are represented in the thalamus. 



The Corpus Striatum. — Lesions of this body are said to be 

 associated with a rise in temperature ; hence it has been looked 

 upon as governing heat production. Little is known of the 

 subject, but it is supposed that impulses pass to the skeletal 

 muscles, causing an increased production of heat. Develop- 

 mentally the corpus striatum is a part of the cerebral cortex, 

 and not a portion of the old mid-brain. The corpus striatum 

 is interesting clinically on account of the comparative frequency 

 with which it is diseased in the horse. There are no symptoms 

 pointing to cerebral trouble until a day or two before death. 

 It is remarkable the size to which a growth in this body may 

 attain before any symptoms of pressure are shown. These cases 

 should enable the question to be settled of the connection, 

 if any, between the corpus striatum and body temperature. 

 ^Experimental injury of the corpus striatum of the horse was 

 carried out by Colin, who found that a simple puncture caused 

 no inconvenience or interference with locomotion. Three fresh 

 punctures made in the same corpus produced immediate paralysis 

 of the hind-legs, and the animal could only be kept standing with 

 a support under the belly. When walked thus supported, the 

 fore-limbs were quite unaffected, the hind-limbs dragged. If the 

 animal fell, power appeared to be regained in the hind-legs, for 

 he was able to recover the standing position. The paralysis 

 gradually passed away, and the horse was able to stand without 

 assistance. 



