658 PHYSIOLOGY. 



As this tract passes through the germ of the capsule it is known as 

 the geniculate tract: a part of the main motor tract. 



3. The Sensory Tract. Its axons arise in the ganglion of the 

 posterior root and extend from the skin and muscles to the spinal 

 cord, where they divide into an ascending and descending branch. 

 The descending branches arborize about the cells in the gray matter 

 of the cord. The ascending branches in great part ascend in the 

 columns of Goll and Burdach and arborize in the cells of the nuclei 

 of Goll and Burdach. From the nuclei of Goll and Burdach a sec- 

 ond series of axons pass under the name of the fillet or lemniscus or 

 interolivary tract, decussating under the floor of the fourth ventricle 

 and chiefly arborize about the cells of the ventral nucleus of the 

 thalamus. From the ventral nucleus a third set of neuraxons arise 

 and go through the posterior part of the posterior segment of the 

 internal capsule to the ascending parietal convolution. This tract 

 receives also the neuraxons of the sensory nuclei of the cranial 

 nerves running to the cortex, excepting the auditory nucleus. 

 In the internal capsule the motor fibers going to the face are 

 in front; next the arm- and then the leg- 'fibers. Hence lesions 

 occurring in the anterior two-thirds of the posterior limb of 

 the capsule cause motor troubles ; lesions in the posterior third cause 

 sensory troubles. The sensory tract is composed of three neurax- 

 ons: one from the skin to GolFs and Burdach's nuclei, the second 

 from these nuclei to the ventral nucleus of the thalamus, and the 

 third from this ventral nucleus to the cortex. Pain and temperature 

 sensations travel through the gray matter. Some sensory impulses 

 can travel by way of the cerebellum to the cerebrum. 



Blood-supply of the Brain. The brain is freely supplied with 

 arteries. The brain with its enveloping membrane is said to receive 

 fully one-fifth of the entire quantity of blood within the body. 



The brain with its adnexa is supplied by the two vertebrate and 

 the two internal carotids, with their numerous branches. These 

 principal vessels form a free anastomosis at the base of the brain, 

 known as the circle of Willis. The circle is composed of the tip of 

 the basilar, the two posterior cerebrals, the two posterior communi- 

 cating, the tips of the two internal carotids, the two anterior cere- 

 brals, and the anterior communicating, which connects the two 

 anterior cerebrals. 



The nucleus caudatus and the nucleus lenticularis are almost 

 exclusively supplied by the middle cerebral artery, whose branches 

 pass through the foramina of the anterior perforated space. The 





