88 ANATOMY AND PHYSIOLOGY. 



called ventricles, one of which is seen in Fig. 32, /, there is con- 

 tinually poured out a clear fluid, which in the healthy state, is im- 

 mediately absorbed; but in a diseased state, this sometimes 

 accumulates until it amounts to gallons, forming one variety of the 

 disease called hydrocephalus, or water in the head. 



The spinal marrow is found to be composed of six columns, as 

 represented in the Fig. Two are anterior, two lateral, and two 

 posterior. These columns, again, when minutely examined, are 

 found to consist of bundles of fibres, that can be traced upwards 

 into, and are found to be continuous with, similar fibres composing 

 the brain and cerebellum. The upper portion of the spinal mar- 

 row (Figs. 32, c, 33,/), which receives the name of the medulla 

 oblongata, is composed, 1st, of two parts called the corpora pyra- 

 midalia, which appear to be chiefly continuous with the anterior 

 columns of the spinal cord and to run upwards to the cerebrum ; 

 2dly. of two similar* parts, called the corpora olivaria, chiefly con- 

 tinuous with the lateral columns of the spinal cord, and likewise 

 principally running up the cerebrum ; and, 3dly, of two other parts, 

 called corpora restiformia, behind the corpora olivaria, continuous 

 with the posterior spinal columns, and chiefly running to the cere- 

 bellum. The two lobes of the cerebellum are also connected with 

 each other by a part called the bridge of Varolius. 



These descriptions are necessary to make intelligible the func- 

 tions of the different parts of the nervous system. We shall now 

 state a few of these. When the spinal marrow is divided in the 

 loins, sensation and all power of voluntary motion are immediately 

 lost in the lower extremities ; when the spinal cord is divided above 

 where the nerves (Fig. 33, g,) come off to the arms, the latter, and 

 all the parts below, suffer in the same manner, but the animal can 

 still breathe ; when the medulla oblongata (Fig. 33,/,) is divided 

 or injured, respiration immediately ceases, and death of course is 

 instantaneous. If, again, the division is made above the medulla 

 oblongata, and below the bridge of Varolius, respiration continues, 

 and the animal may live for a longer or shorter time. Chossat, a 

 French physiologist, who performed some experiments of the latter 

 kind on dogs, thinks they die from an inability to keep up their 

 natural temperature. Tortoises, however, in which the brain has 

 v been taken out, have lived for four or six months afterwards. The 

 brain of a young puppy was removed, and it not only continued to 

 breathe, but also sucked, when applied to the teat, or when the 

 finger, moistened with sugar, was put in its mouth. There have 



