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14 PHYSIOLOGY. 



The Spinal Marrow. 



A pulpy cord, white without, gray within ; lodged in the 

 vertebral canal ; extending from the base of the brain to the 

 lumbar portion of the vertebral column, where it is divided 

 into a great number of filaments called the cauda equina, from 

 its fancied resemblance to a horse's tail. 



The Nerves. 



White cords extending from the base of the brain and from 

 the spinal marrow to the muscles, and to the surface of the 

 general coverings of the body, to form the organs of sense. 

 (PL 2, fig. A, and PL 3, fig. B.) 



The Sense of Touch. 



Of this the seat is the skin. The skin is composed of the 

 epidermis (PL 1, fig. 1, b, and PL 2, fig. 2, e), the nervous 

 and colouring tissue (PL 1, fig. 1, a, and PL 2, fig. 2, d), the 

 dermis (PL 1, fig. 1, c, and PL 2, fig. 2, c), and the piliferous 

 (hair producing) bulbs, and is supplied with blood vessels 

 (PL 2, fig. 2, a). 



The Sense of Taste. 



Of this the instrument is the tongue, or rather the mucous 

 membrane covering the tongue. 



The Sense of Smell. (PI. 2, fig. 3.) 



The apparatus of smell is composed of the olfactory nerve 

 and pituitary membrane covering the nasal fossce, including 

 the spongy bones, the partition of the nose (vomer) and car- 

 tilages with the sinuses (fig. 3, a). This sense is excited by 

 the action of odours upon this apparatus. 



The Sense of Hearing. (PI. 2, fig. 4.) 



This apparatus is composed of the external ear, including 

 the pinna or pavilion (a, b, d) and the external auditory canal 

 (c) ; the middle ear which includes the cavity of the tympa- 

 num (h) separated from the external ear by the membrane of 

 the tympanum (g); the chain of small bones, viz., the stapes, 

 the orbicular e, the incus and the malleus ; the muscles which 

 move these bones; and the eustachian tube (k); the internal 

 ear, embracing the vestibule, where we find the oval window, 

 fenestra ovalis, the opening of the semicircular canals (1), anr! 

 the opening of the cochka\ the semicircular canals (m); the 



