THE ERGOT AND CHESTNUT THE ORGAN OP TASTE 895 



The Ergot and Chestnut 



_ The ergot is a small mass of horn which is situated in the tuft of hair at the 

 flexion surface of the fetlock. It is commonly regarded as the vestige of the second 

 and fourth digits of extinct equidse, and hence is absent in cases in which these 

 digits are developed. A small fibrous band, 3 to 5 mm. in width, extends downward 

 and slightly forward from the fibrous basis of the ergot on each side, crosses over the 

 digital vessels and nerves very obliquely, and blends below with the digital fascia 

 and the digital cushion. It is known as the ligament or tendon of the ergot (Fig. 

 672). 



The term chestnut is applied to the masses of horn which occur on the medial 

 surface of the forearm, about a handbreadth above the carpus, and on the distal 

 part of the medial face of the tarsus. They have an elongated oval form and are 

 flattened. They are regarded usually as vestiges of the first digit. That of the 

 hind limb is absent in the donkey and very small in the mule. 



These horny vestiges are quite variable in form and size and are correlated with the fineness 

 or coarseness of the integument in general. The supracarpal chestnut is about IJ^ to 2J/2 inches 

 long, oval in outUne, the proximal end being pointed; it overlies the flexor carpi radialis at a 

 quite variable distance above the carpus, and hence should not be used as a surgical landmark. 

 The tarsal chestnut hes at a point behind the lower part of the medial ligament of the hock. When 

 weU developed it is about 2 to 2}-^ inches long, broad below and produced above to form a long 

 pointed end, with a short blunt anterior process. They are composed of horn somewhat hke that 

 of the frog. 



Organ of Smell 



The peripheral part of the ' olfactory apparatus or organ of smell (Organon 

 olfactus) is that part of the nasal mucous membrane which was referred to in the 

 description of the nasal cavity as the olfactory region; this (Regio olfactoria) is 

 limited to the ethmoturbinates and the adjacent part of the dorsal turbinate and 

 the septum nasi, in which the fibers of the olfactory nerve ramify. It is distin- 

 guished by its yellow-broAvn color, thickness, and softness. It contains character- 

 istic tubular olfactory glands, which are lined by a single layer of pigmented cells, 

 and a neuro-epithelium, the olfactory cells, the central processes of which extend 

 as non-medullated fibers to the olfactory bulb. 



The epithelium is non-ciliated and is covered by a structureless Umiting layer. It consists 

 essentially of three kinds of cells, supporting, basal, and olfactory. The supporting cells are of 

 long columnar form above and contain pigment granules; below they taper and often branch, 

 and" their central processes unite with those of adjacent cells to form a protoplasmic network. 

 The Ijasal cells are branched and he on a basement membrane. The ohactory cells are situated 

 between the supporting cells; they have the form of long narrow rods, with an enlarged lower 

 part which is occupied by the nucleus. The peripheral end pierces the hmiting membrane and 

 bears a tuft of fine, hair-hke cilia (olfactory hairs) . A central process extends from the nucleated 

 pole of the cell to the olfactory bulb as a non-meduUated olfactory nerve-fiber. 



The vomero-nasal organ (Fig. 452) lies along each side of the anterior part 

 of the lower border of the septum nasi. It communicates with the nasal cavity 

 through the naso-palatine canal. It consists of a tube of hyaline cartilage lined 

 with mucous membrane; a small part of the latter along the medial side is olfactory 

 in character. 



The Organ of Taste 



The peripheral part of the gustatory apparatus (Organon gustus) is formed by 

 the microscopic taste buds (Calyculi gustatorii), which occur especially in the foliate, 

 fungiform, and vallate papillae, in the free edge and anterior pillars of the soft 

 palate, and the oral surface of the epiglottis. The taste buds are ovoid masses, 



