STEtrCTtJKE OF THE HORSE. 129 



nerve and binds its bundles together. It contains blood vessels, 

 lymphatics, connective tissue, cells, and adipose tissue. Nerves 

 which convey impressions to the centers are termed centripetal 

 or afferent; those which transmit stimuli from the centers to the 

 various organs are termed centrifugal or efferent, while those 

 which pass from one center to another are called inter-central. 

 Centrifugal are called motor, supplying muscles; vasomotor, 

 supplying the muscular fibers of the blood vessels; secretory, 

 supplying glandular epithelium; inhibitory, modifying the ac- 

 tions of the nerve centers; trophic, regulating the nutrition of 

 a part. 



Centripetal nerves, which convey common sensation, pain, 

 touch, etc., are termed sensory. When they convey impressions 

 peculiar to an organ, as the nerves of sight and hearing, they 

 are known as nerves of special sense. Nerves conveying im- 

 pressions which lead to the stimulation of motor nerves are 

 termed excito-motor; if to that of secretory nerves, excito- 

 secretory; and if to that of inhibitory nerves excito-inhibitory. 

 This reflection of nervous impulse from one nerve to another is 

 known as reflex action. There are many things difficult and 

 sometimes inexplicable about the nervous system and its opera- 

 tions. 



The cerebro-spinal system has for its center the cerebro- 

 spinal axis, consisting of the brain and spinal cord, which, like 

 their coverings or meninges, are continuous with each other. 

 The brain of the horse corresponds to the cavity in which it is 

 placed. It is a flattened oval, divided into two parts, one much 

 larger than the other — the cerebrum, or larger portion, and the 

 cerebellum, or smaller portion. In the horse the cerebrum is 

 below the cerebellum, and occupies the anterior portion of the 

 cranial cavity. It is ovoid in shape, with an irregular flattened 

 base, and consists of lateral halves or hemispheres, separated by 

 a longitudinal fissure. The cerebellum or lesser brain is lodged 

 in the posterior part of the cranial cavity, immediately above the 

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