THE ERGOT AND CHESTNUT—THE ORGAN OF 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 equide, since it 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. 
572). 
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 excrescences are quite variable in form and size and are correlated with the fine- 
ness or coarseness of the integument in general. The supracarpal chestnut is about 11 to 24% 
inches long, oval in outline, 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 lies at a point behind the lower part of the medial ligament of the hock. When 
well developed it is about 2 to 214 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 like 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-brown color, thickness, and softness. It contams 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 limiting 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 basal cells are branched and lie on a basement membrane. The olfactory 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 limiting 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-medullated 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 peripherai 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 papille, in the free edge and anterior pillars of the soft 
palate, and the oral surface of the epiglottis. The taste buds are ovoid masses, 
