548 THE NERVOUS SYSTEM 



Corpora Striata. The corpora striata are situated in front and to 

 the outside of the optic thalami, partly within and partly without the lateral 

 ventricles. 



Each corpus striatum consists of two parts: An intra ventricular portion, 

 the caudate nucleus, which is conical in shape, with the base of the cone for- 

 ward -(this consists chiefly of gray matter), and an extraventricular portion, the 

 lenticular nucleus, separated from the other portion by the internal capsule. 

 The lenticular nucleus is shown in a horizontal section of the hemisphere to 

 consist of three parts, the two internal called globus pallidus major and minor, 

 and the outer called the putamen. 



The cells of the corpora striata are somewhat evenly distributed, and not 

 grouped in nuclei. Their axones pass for the most part into the internal 

 capsule. It is doubtful if these ganglia have any direct anatomical relations 

 with the cortex of the brain, but they are intimately connected by fibers to and 

 from the optic thalami, and are connected with the substantia nigra (Flechsig). 

 These nuclei are developed from the walls of the embryonic brain tube and 

 are probably therefore homologous with the areas of the cortex. Their lesion 

 is said to be accompanied by disturbance in muscular coordination. Lesion 

 of the left lenticular nucleus is said to cause some disturbance in the power of 

 speech, though this has not been observed in the case of the right nucleus. 

 Lesions of the corpora striata produce disturbances in heat regulation, causing 

 a rise of body temperature, the rise amounting to as much as 2 or 3 C. in 

 the rabbit. The rise of temperature in man after lesion of the corpus striatum 

 on one side is said to be chiefly on the opposite side of the body (Kaiser). 



THE CRANIAL NERVES. 



The cranial nerves consist of twelve pairs; they appear to arise (superficial 

 origin) from the base of the brain in a double series, which extends from the 

 under surface of the anterior part of the cerebrum to the lower end of the 

 medulla oblongata. Traced into the substance of the brain and medulla, the 

 roots of the nerves are found to take origin from various masses of gray matter. 



The roots of the first or olfactory and of the second or optic nerves will be 

 discussed elsewhere. The third and fourth nerves arise from gray matter 

 beneath the corpora quadrigemina ; and the roots of origin of the remainder of 

 the cranial nerves can be traced to gray matter in the floor of the fourth ventri- 

 cle, and in the more central part of the medulla, around its central canal, as low 

 down as the decussation of the pyramids. 



According to their several functions the cranial nerves may be thus 

 arranged : 



Nerves of special sense. .. . \ Olfactor y, Optic Auditory part of the Glosso- 



( pharyngeal, and part of the Trigemmal. 



Nerves of common sensation. . . The greater portion of the Trigeminal. 



