676 NERVOUS SYSTEM OF THE HORSE 



further back they are connected by strands of gray matter which intersect the in- 

 ternal capsule. 



The amygdaloid nucleus (Nucleus amygdalae) (Fig. 506) is an ovoid mass of 

 gray matter situated external to the ventral horn of the lateral ventricle and below 

 the posterior part of the lenticular nucleus. Some fibers of the stria terminalis 

 are connected with it. 



The internal capsule (Capsula interna) is a broad band of white matter situated 

 between the thalanuis and caudate nucleus internally and the lenticular nucleus 

 externally. A sagittal section through the brain shows that it is in great part 

 directly continuous with the basis or ventral part of the cerebral peduncle. It 

 contains most of the so-called projection fibers of the hemisphere, which connect the 

 cerebral cortex with nuclei of other and more posterior parts of the brain. When 

 the fibers of the internal capsule are traced forward it is evident that they spread 

 out in all directions to reach the cerebral cortex. This arrangement, in which the 

 fibers of the corpus callosum participate, is termed the corona radiata. 



The internal capsule also contains fibers which connect the corpus striatum with the thala- 

 mus. These are termed the thalamo-striate and strio-thalamic fibers respectively, according to 

 the direction in which they conduct impulses. 



The fibers of the stria terminalis connect the amygdaloid nucleus with the septum pelluci- 

 dum and trigonum olfactorium. It is therefore probably part of the complex connections be- 

 tween the primary and secondary olfactory centers. 



The Cranial Nerves 



The cranial or cerebral nerves (Xn. cerebrales) comprise twelve pairs which 

 are designated from before backward numerically and by name. Their number, 

 names, and functional characters are given in the subjoined table: 



I. Olfactory Sensory (Smell) 



II. Optic Sensory (Sight) 



III. Oculomotor Motor 



IV. Trochlear IVIotor 



V. Trigeminal Mixed 



VI. Abducent Motor 



VII. Facial Mixed 



VIII. Auditory Sensory (Hearing and Equilibration) 



IX. Glosso-pharyngeal Mixed 



X. Vagus or Pneumogastric Mixed 



XI. Spinal accessory Motor 



XII. Hypoglossal Motor 



THE FIRST OR OLFACTORY NERVE 



The olfactory nerve (N. olfactorius) is peculiar in that its fibers are not aggre- 

 gated to form a trunk, but are connected in small bundles with the olfactory bulb. 

 They are non-medullated, and are the central processes of the olfactory cells which 

 are situated in the olfactory region of the mucous membrane of the nasal cavity. 

 This region is distinguished by its brown color and comprises most of the lateral 

 mass of the ethmoid, a small adjacent area of the superior turbinal, and the corre- 

 sponding surface of the septum nasi. The nerve-l)undlcs are inclosed in sheaths 

 derived from the membranes of the brain and pass through the foramina of the 

 cribriform plate to join the convex surface of the olfactory bulb. Some fibers come 

 from the vomero-nasal organ of Jacobson. 



THE SECOND OR OPTIC NERVE 



The optic nerve (X. oj^ticus) is composed of fibers which are the central pro- 

 cesses of the ganglion cells of the retina. The fibers converge within the eyeball to 



