390 
T. F. WINCHESTER. 
4. 1 he tavorite seat of the worm-aneurism is the trunk 
the anterior mesenteric artery, directly at its origin from t: 
abdominal aorta. Most frequently that part of the arten 
trunk is dilated from which the arteria ilea, csecales and coli 
inferior (arteria ileo-casco-colica) arise, less frequently t! 
arteria colica superior at its origin, and the arteries of tl 
caecum and colon in their course in the meso-caecum and mes 
colon. The verminous aneurism also occurs in the coeliac £ 
tery (Bauchschlagader), in the posterior mesenteric artei 
(Gekrosarterie) in the renal artery, and in the abdomin 
aorta. A horse is not infrequently afflicted with sever 
aneurisms of this kind at one and the same time. Thus 
one case (described by Bollinger) there were six of the 
aneurisms affecting the abdominal aorta and its branches 
the same horse. The verminous aneurism may occur fro 
the sixth month of life onwards, and with increasing age; tl 
number of horses free from such aneurisms becomes conti 
ually smaller. 
5. The aneurism varies in size from that of a pea to that < 
a man’s head. The dilation is, as a rule, equal on all side 
the form being usually thumb-shaped or bottle-shaped, passin 
into that of a cone or long oval figure. This general config 
ration is principally due to the free and movable situation <j 
the anterior mesenteric artery. 
6. In contrast to aneurisms in man, the walls of the worn 
aneurism in the horse are almost without exception indurate* 
In addition to the mesenteric connective tissue, all the arteri, 
coats, and especially the tunica media, generally take part i 
this induration. The hypertrophy of the media, which slant 
unique in respect of what is known of arterial disease, form 
a compensatory action of the arterial wall, analogous to th 
muscular hypertrophy of the heart in valvular disease. Th 
change in the media points to the fact that in the develoj 
ment of aneurism in man the early disturbance of the nutr 
tive process in the tunica media is not a less essential facte 
than the degeneration of the tunica intima. 
The changes in the intima are the least constant. The, 
present all stages of progressive and retrogressive metamoi 
