198 MR. youatt’s veterinary lectures. 
and nasal bones; an irregular suture connects the frontal and 
the nasal bones; and we at length arrive at the other frontal 
bone, and the suture, with the consideration of which we started. 
There is but one muscle properly belonging to the frontal 
bone, which is the levator palpebrse superioris—the raiser or 
corrugator of the upper eyelid, which is a very thin muscle, 
arising from an aponeurotic expansion on the forehead, and is 
inserted into the superior part of the upper eyelid, towards the 
inner angle. 
The frontal bones differ materially in form and development 
in different breeds of horses. As a broad and angular forehead 
in man is supposed to be connected with courage and intellect, 
so the angular projection of the orbital processes, or, in other 
words, the breadth of the forehead, distinguishes the spirited and 
noble blood-horse from the dull and stupid dray-horse. —[The 
Lecturer here produced some drawings of the heads of different 
breeds of horses, and also the crania of the blood-horse, the 
half-bred, and the cart-horse, and directed his class to compare 
the long face and narrow forehead of the last, with the short 
face and expanded forehead of the first, and the medium cha¬ 
racter of the second.] 
The frontal bone, through the greater part of its extent, con¬ 
sists of two plates, or tables, irregularly separated from each 
other: the inner plate recedes, and thus the frontal sinuses , or 
cavities, are formed. They are perfectly divided from each 
other by a thin plate dipping down from each, at and along the 
frontal suture, and uniting to form a septum of some thickness. 
This septum appears, in situation, to be a continuation of that 
of the nose. There are other imperfect septa, which divide the 
sinuses into cells, yet still communicating with each other. The 
frontal sinuses extend from an imaginary line drawn from the 
middle of one orbital fossa to the other, to another line supposed 
to be drawn from the inner angle of one eye to the opposite one. 
They are deepest at the centre, and there sometimes more than 
an inch in depth; the point of greatest depth is at the middle of 
an imaginary line drawn from one foramen super-orbital to the 
other. In young animals, the sinuses are very small; but they 
increase with the age of the animal, until, in an old horse, they 
extend through the whole of the frontals and a portion of the 
parietals. 
Although the frontal sinuses do not communicate with each 
other, they communicate with the maxillary sinuses, and those of 
the sphenoid and mthmoid bones, and, by means of the max¬ 
illary sinus, indirectly with the nasal cavity, into which this 
sinus opens under the superior turbinated bone, by a kind of val¬ 
vular aperture. The frontal sinuses are lined by a continuation of 
