OF CATTLE AND SHEEP. 271 
laterally ; which gives the peculiar breadth of forehead and pro¬ 
minence of eye to the sheep. This process, occupying the supe¬ 
rior and exterior portion of the orbitar ring, presents forwards a 
sharper edge than in the ox, while it has comparatively less depth 
and strength ; except that which it acquires from the more 
perfect arched form of the process, and the roundness of the 
orbit, in this animal. 
The orbitar process abuts upon the superior bifurcation of the 
malar bone, as it does in the ox, and has no connexion with the 
temporal bone; and, deep in the temporal fossa, it is almost cut 
off from connexion with it by the curious lateral development of 
the parietal bones in these animals. 
Although the frontal sinuses of the sheep, and even of the 
horned breeds, are far less extensive than those of the ox, yet 
this animal is subject to an excessive annoyance, from which the 
ox is comparatively exempt. There is a fly of the Diptera order 
(flies with two wings, and behind them two globular bodies, sup¬ 
ported on slender pedicles, called, and properly, poisers), the 
(Estrus ovis, the Gad-fly of the sheep. It assumes its perfect 
and winged form in June and July, and then it is an intolerable 
nuisance to the sheep, especially in woody countries, or in the 
neighbourhood of copses. If only one appears, the whole flock is 
in the greatest agitation. They gather together with their heads in 
the centre, and their muzzles buried in the sand if they can find 
any, and are in continual motion to guard their noses against the 
attacks of their puny enemy. The (Estrus, impelled by powerful 
instinct, endeavours to deposit its eggs on the inner margin of the 
nose. By the warmth and the moisture they are almost imme¬ 
diately hatched, and the larvae or little maggots crawl up the 
nose, and find their way to the residence that nature designed for 
them. As the eggs of the horse gad-fly, being licked from the 
parts on which they are deposited, and hatched by the warmth 
and moisture of the tongue, are conveyed into the stomach 
with the saliva, or with food, and attach themselves to, and live 
on, the inner coat of the stomach, until they are ready for their 
transformation, so the eggs of the gad-fly of the sheep, being de¬ 
posited on the edge of the nostril, are quickly burst, and the little 
worms crawl up the nose. In the act of passing up the nose 
they seem to give dreadful annoyance, for the sheep gallops furi¬ 
ously hither and thither, and snorts violently, and seems almost 
mad. Having traced their circuitous course, through the aper¬ 
ture under the upper turbinated bone into the maxillary sinus, 
and thence into the frontal one, the larva fixes itself on the 
membrane of the sinus by means of two tentacula or hooks which 
grow from the side of its mouth, and there it remains feeding on 
