HOW THE ANIMAL BODY IS FORMED I9 



The Muscular System of Farm Animals. — The 



muscular system is too elaborate, the number of 

 muscles too great, and their modifications for dif- 

 ferent purposes too complex for consideration in 

 detail in the present volume. All muscles are 

 either striped or unstriped (as examined under the 

 microscope), according as they are under the im- 

 mediate control of the will or not. The heart 

 muscle forms an exception, for it is striped though 

 involuntary. The essential characteristic of muscle 

 fibers is contractility, which they possess in high 

 degree. The typical striped muscles are concerned 

 in locomotion, being attached at either end to a 

 bone and extending across some movable joint. 

 The most important unstriped muscles are found in 

 the walls of the intestines and blood vessels. 



The Nervous System. — In so far as our present 

 purposes are concerned, the nervous system may 

 be disposed of in a few words. The central nerv- 

 ous system consists of a brain and spinal cord. 

 The microscopic elements of this tissue are pecu- 

 liarly modified cells, consisting of a central body, 

 from which fibers run in two or more directions. 

 The cell bodies constitute the gray matter, and the 

 fibers the white matter of the brain and spinal cord. 

 The gray substance is Inside the spinal cord and on 

 the surface of the brain, constituting the cortex. 

 The most important parts of the brain are the 

 cerebrum, optic lobes, cerebellum, and medulla. 

 There are twelve pairs of cranial nerves originat- 

 ing in the brain and controlling the special senses, 

 movements of the face, respiration, and pulse rate. 

 From each segment of the spinal cord a pair of 

 spinal nerves arises, each of which possess both 

 sensory and motor roots. The sympathetic nervous 

 system consists of a trunk on either side, running 



