192 



THE POPULAR EDUCATOR. 



from which branches are given off to supply the parts about the 

 neck and the side of the head. One large branch, called the 

 phrenic, descends into the chest to supply the diaphragm. The 

 lower cervical and the first dorsal nerves form another plexus, 

 which supplies the upper extremity and some of the muscles of 

 the thorax. 



The dorsal nerves supply the parietes of the thorax and 

 abdomen, and some of the muscles of the back. 



The lumbar nerves form a plexus, which gives off branches to 

 the lower portion of 

 the abdomen and front 

 part of the thigh. 



The sacral nerves 

 form a plexus, the 

 branches of which 

 supply the posterior 

 portion of the body 

 and thigh, and both 

 front and back of the 

 leg and foot. 



Connected to the 

 epinal cord by the 

 medulla oblongata is 

 the chief centre of the 

 nervous system, the 

 brain. This is the seat 

 of the highest faculties 

 of the animal life; 

 from it are issued the 

 mandates of the will, 

 and by it cognisance is 

 taken of external ob- 

 jects and sensations. 

 Its comparative size is 

 much greater in man 

 than in any of the 

 lower animals, and its 

 absolute size is greater 

 than any save those of 

 the whale and the 

 elephant. Its usual 

 weight in the male 

 adult is about 50 

 ounces, that of the 

 female being .about 46 

 ounces. It increases 

 in size rapidly up to 

 the seventh year, more 

 elowly till between the 

 ages of thirty and forty, 

 when it attains its 

 maximum ; from this 

 point it gradually de- 

 creases again at about 

 the rate of an ounce 

 for every ten years. 

 The size of the brain VIII. VIEW OF SPINAL CORD, SHOWING ITS CONNECTION WITH THE BRAIN. IX. BASE 



bears, no doubt, some 



relation to the intel- Eefs. to Nos. in Figs. VIII. 1, the cerebrum, or brain proper; 2, the cerebellum, or 



lectual power of the 

 individual; for whilst 

 the brain of Cuvier, 

 the great French natu- 

 turalist, weighed 64 

 ounces, and Dr. Aber- 

 cromby's 63 ounces, the brain of an idiot in very few cases organic life. In harmony with this view is the fact that its 



of nerves, the functions of which wo must now consider. The 

 first pair are the nerves of smell, or olfactory : the second are 

 the optic, or nerves of sight : the third, fourth, and sixth are 

 the motor nerves of the muscles of the eyeball : the fifth is a 

 compound nerve which resembles the spinal nerves in having 

 two roots ; it is a nerve of special sense, inasmuch as it is one 

 of the nerves of taste ; it is a sensory nerve supplying the head 

 and face, and it is the motor nerve of the muscles of masti- 

 cation : the seventh is also a compound nerve, one-half of 



it being the auditory 

 nerve, whilst the other 

 is the motor nerve 

 to the muscles of the 

 face : the eighth is 

 composed of three 

 nerves, one of which, 

 the glosso-pharyngeal, 

 is the other nerve of 

 taste, the sensory nerve 

 to some of the parts at 

 the upper portion of the 

 throat, and the motor 

 nerve to the muscles of 

 the same region. The 

 pneumogastric, or 

 vagus, with which is 

 closely connected the 

 spinal accessory, is 

 the most widely dis- 

 tributed of any of the 

 cranial nerves ; it 

 arises specially from 

 the medulla oblongata, 

 and is both the sensory 

 and motor nerve to the 

 organs of voice and 

 respiration, and the 

 motor nerve to the 

 5 pharynx, oesophagus, 

 stomach, and heart. 

 6 The ninth pair are the 

 motor nerves of the 

 tongue. 



The sympathetic 

 system consists of a 

 chain of ganglia con- 

 nected by nerve cords, 

 running down the front 

 of the spinal column 

 and giving off nerves, 

 on several of which are 

 developed secondary 

 ganglia, through which 

 it is closely connected 

 with the branches of 

 the cerebro-spinal 

 system ; it is quite 

 uncertain where the 

 functions of one begin 

 and the other cease, 

 but it is generally 

 believed that the sym- 

 pathetic system is 

 more closely connected 

 with the functions of 



IX. 



OF BRAIN, SHOWING ORIGINS OF CRANIAL NERVES. X. VERTICAL SECTION OF BRAIN. 



little brain ; 3, the medulla oblongata ; 4, the cervical nerves ; 5, the dorsal nerves ; 



6, the lumbar and sacral nerves. IX. 1, the olfactory nerve ; 2, the optic nerve ; 

 3, the third nerve ; 4, the fourth nerve ; 5, the fifth nerve ; 6, the sixth nerve ; 



7, the seventh nerve ; 8, the eighth nerve ; 9, the ninth nerve ; 10, medulla 

 oblongata; 11, cerebellum. X. 1, the cerebrum; 2, the cerebellum. 



exceeds 23 ounces. 



The brain consists of two great parts the cerebrum, or brain 

 proper, occupying the front and upper portion of the skull ; and 



chief branches are distributed to the viscera of the thorax 

 and abdomen, and to the blood-vessels. 



This completes our examination of the human body as a 



the cerebellum, or lesser brain, which lies underneath the pos- j whole, and we must now proceed to investigate those functional 

 terior part of the cerebrum in the occipital fossa at the back ', processes which are necessary for the existence of the organism. 

 of the skull. They are each divided into two lateral halves or i These may be roughly divided into three digestion, circulation, 

 hemispheres, and each hemisphere is divided into lobes by and respiration. We shall take them in this order, and 

 fissures caused by the dipping in of the brain substance. The under the first heading shall first examine the parts concerned 

 bulk of both is composed of the white nervous matter, over j in the process, then say a few words on the general subject of 

 which is spread layers of grey matter, the latter here being food, and finally trace the food through the various changes it 



external. 



From the under surface of the brain are given off nine pairs the system. 



undergoes in the digestive canal to its ultimate assimilation by 



