408 ANDROPHTSICS. 



them, would far transcend our limits ; but we may observe that they 

 are mostly named from the organs to which they belong, and the kind 

 of motion which they are intended to produce ; or from their struc- 

 ture, or position. Thus, those which cause the bending of the 

 limbs, are called flexors, as the flexor carpi radialis, serving to bend 

 the wrist and fore arm ; while those which act to straighten the limb 

 by their contraction, are called extensors, as the extensor carpi ulna- 

 ris, on the outer or upper side of the fore arm, serving to bend the 

 hand backward. Thus too, we have the levator menti, or muscle 

 which, by contracting, raises the chin; the orbicularis oris, serving to 

 contract the mouth ; and the rectus superior, which, by contracting, 

 raises the eye. 



3. Neurology, is that division of Anatomy which treats of the 

 nerves, and the nervous system ; including the organs of sensation ; 

 among which are the eye and the ear. The nervous system, con- 

 sists of the brain ; the spinal marrow ; the nerves ; and the nervous 

 ganglia. The brain, situated within the skull, is regarded as the 

 immediate seat of the intellect ; or the organ by means of which we 

 perceive, feel, reason, and will. It is a soft, pulpy substance, and 

 consists of the cerebrum, made up of convolutions or folds, occupy- 

 ing the whole upper part of the skull ; the cerebellum, or smaller 

 brain, occupying the lower and back part; the pons Variolii con- 

 necting the preceding, at the centre of the brain ; and the medulla 

 oblongata, or oblong marrow, extending from the pons Variolii down 

 to the spinal marrow. These parts together are enveloped by mem- 

 branes, and are sometimes called the common sensorium, considered 

 as the seat of sensation and volition. The medulla spinalis, or spi- 

 nal marrow, is a continuation of the medulla oblongata, extending 

 down the interior of the spine, and terminating in a complex nerve 

 called cauda equina. 



The nerves, are white cords, usually consisting of bunches of 

 filaments, often interweaving with each other, and connected by cellu- 

 lar tissue. All the cerebral and spinal nerves, are connected with the 

 brain, either directly, or by means of the spinal marrow : and they 

 are found to consist of two classes ; nerves of sensation, by which 

 the mind perceives or feels ; and nerves of volition, which are con- 

 nected with the muscles, and serve to produce motion : but these two 

 kinds are generally associated, forming compound nerves. They 

 usually proceed in pairs, branching as they diverge, towards the 

 extremities of the body : those designed to produce motion being 

 usually the largest. There are twelve pairs of cerebral nerves, pro- 

 ceeding directly from the brain, and chiefly distributed ever the head; 

 and thirty pairs of spinal nerves, proceeding from the spinal marrow 

 to the various parts of the body. 



The ganglionic system consists of ganglia, or knots, in which 

 several nerves unite, forming what some anatomists have termed 

 *' diminutive brains 1 ' : but although these ganglia have a connexion 

 with the nerves proceeding from the brain, and may produce sen- 

 sation, they are more or less independent of volition, and hence may 

 be called nerves of instinctive action : their use being to cause those 

 muscular motions, of digestion, respiration, and circulation, which 



