A BACTERIOLOGICAL STUDY OF EQUINE FISTULA. 
341 
of the dorsal vertebrae and the muscles which cover them. The 
skin lined inside with cellular tissue, more condensed toward 
the median line than on the sides, where it is loose, the trape¬ 
zius muscle thick and muscular in its upper portion, where it 
lies over the external surface of the scapula, and its cartilage 
of prolongation, thin and aponeurotic interiorly; the rhom- 
boideus muscle, which is separated from the second plane on its 
external surface by a layer of loose cellular tissue, and is lined 
on its external face with a yellow elastic band inserted on the 
inner face of the cartilage of prolongation of the scapula (this 
band is especially liable to attacks of necrosis); the superior 
portion of the anterior small serratus muscle, which is formed 
by a broad aponeurosis attached to the superior extremity of 
the spinous processes of the vertebras, the anterior portion of 
the ilio spinalis muscle; the deepest of these planes resting 011 
the faces of the long spinous processes of the vertebras is formed 
by the transverse spinal muscles of the back. 
The Poll-evil is a fistulous ulcer, situated on the supero- 
posterior portion of the head, immediately behind the ears. At 
first it may be recognized as a soft, fluctuating tumor, surrounded 
by an inflammatory swelling, with enlargement of the superior 
cervical lymphatics and the superficial veins of the neck. 
The tumor that can be felt may be a cyst filled with serum, 
or it may be filled with a purulent substance, just as the case 
may happen to remain aseptic, or become infected with micro¬ 
organisms; if a serous cyst is formed it may become infected 
during formation by micro-organisms entering the serum which 
forms or makes up the cyst. 
Fistulous withers resembles Poll-evil in every particular 
except its location. 
If we get the anatomy clearly in our minds, we will have a 
good idea of the intricate disposition of its many parts, with 
their relation to the disease which attacks them, and it also 
explains the tendency of the purulent material gravitating and 
collecting between the muscles, and contributing to the forma¬ 
tion of the ailment known as a true “diseased withers,” with 
