900 



PRACTICE OF AGRICULTURE. 



Part III. 



SuBSECT. 6". The Head generally. 



5692. The parts of the head are external and internal ; some of these have been 

 touched on, as the integuments, &c. : such as have not will follow in the order of 

 their magnitude or situation. 



5693. The brain of the 

 horse {fig. 616 a, b, c), is 

 contained within the hol- 

 low of the skull, and is 

 surrounded by two cover- 

 ings, the dura; and pia 

 mater, between which 

 lies a third membrane 

 called the tunica arach- 

 noidea. The duplica- 

 tures of these membranes 

 are called septa and falx. 

 The brain is divided into 

 three portions, the cere- 

 brum, cerebellum, and 

 medulla oblongata. The 

 cerebrum, or greater 

 brain (a), is divided 

 into two hemispheres and 

 two lobes ; it has an outer 

 or cortical substance, and 

 an inner, the substantia 

 a1ba,or medullary matter. 

 The cerebellum, or lesser 

 brain (A), is contained 

 within the occipital bone, 

 and is in the horse placed 

 superiorly and posterior- 

 ly to the cerebrum. It 

 is less than the cerebrum, 

 and is divided into four 

 lobes, and like the form- 

 er is composed of two 

 substances, a cortical and 

 a medullary. The me- 

 dulla oblongata (c) is a 

 medullary continuation 

 of the cerebrum and ce- 

 rebellum, and is conti- 

 nued upwards and back- 

 wards to the edge of the 

 ferumen magnum of the 

 OS occipitis, to be conti- 

 nued under the name of 

 spinal marrow. The 

 medulla spinalis,or spinal 

 marrow {k), is a direct 

 continuation of the me- 

 dulla oblongata, and like 

 that is composed of a 



cortical and medullary part. It has lately been discovered to be hollow in the horse, ox, sheep, hog, and 

 dog. It leaves the skull by the great foramen of the occipital bone, and is continued backwards in a 

 bony canal formed by the vertebra, giving ofFin its passage the spinal nerves in pairs. The brain presents 

 four cavities called ventricles, it has also many prommences, and peculiarities, which our limits will 

 not admit of noticing, but which is less necessary, as in no part of brute anatomy is the analogy 

 so close to the human as in the brain of the horse. "With the exception of the situation, to describe the 

 one is to portray the other. 



SuBSECT. 7. The Ear, 



5694. The number and situation of the ears of the horse are sufficiently known. The internal parts 

 do not differ from those of the human, but the outer are adapted to his situation and habits. These 

 exterior parts are composed of , the skin, the outer hair, the cartilages, and the muscles by which they 

 are moved. The skin within the ears is furnished with sebaceous glands, which secrete a bitter matter, 

 noxious to insects ; and further to guard against these, it is filled with hair; which the false taste of 

 grooms induces them to remove, and thus to expose the animal to dust, hail, rain, and insects. 



5695. The form of the ear is dependent on the concha cartilage, which is found pointed and small in 

 the Arabian, but large and broad in the heavy breeds. The cavity within the concha is thrown into folds 

 throughout, which increases its surface, and reflects the sonorous waves. This outer ear is attached 

 to the internal, by connecting cartilaginous portions and appropriate ligaments. The parts of the internal 

 ear are, the meatus auditorius internus, or passage; the membrana tympani, or separating membrane 

 between the external and internal parts; the tympanum, drum, or barrel of the oar; and the labyrinth. 

 The eustachian tube is an opening at the upper and anterior edge of the hollow of the tympanum, forming 

 a duct which is in part bony, and in part cartilaginous ; extending from the tympanum to a large and 

 peculiar cavity at the posterior part of the nasal fossa. 



5696. The sense of hearing is formed through the medium of the expansion of the soft portion of the 

 auditory nerve over the internal ear ; sounds, therefore, entering the cavity of the concha, are reflected 

 alternately from its sides into the tympanum, whose oscillations are imparted to the brain. 



SuBSECT. 8. The Eye and its Appendages. 



5697. The appendages to the eye are first, a funnel-shaped cavity formed by the con- 

 currence of the bones of the skull, called the orbit, not placed directly in front as in 

 man, but inclining laterally, to enable the animal to embrace a larger field of view. 

 The eyelids are an upper and under, of which the upper is the most considerable, and 



