486 MR. youatt’s veterinary lectures. 
tous connecting bands had passed all round, there would have 
been a looseness and want of strength about the tube that would 
have been exceedingly inconvenient, and not at all adapted for 
the free passage of air through it. The connecting ligament in 
front and on the side, with its oblique fibres in contrary direc¬ 
tions, and the overlapping of the cartilages behind, and they 
bound together also by a ligamentous expansion much less ex¬ 
tensible, will unite all the flexibility and strength that can be 
needed. 
The Transverse Muscle .—If we look within the trachea of the 
horse, we find another very curious structure. At the points at 
which posteriorly the rings begin to bend inwardly, a muscle is 
found stretching across the trachea, and dividing the canal into 
two unequal portions, the anterior one constituting the proper 
air-passage, and the posterior one filled with cellular or reticular 
texture. 
To Mr. Sewell, I believe, we are indebted for first directing our 
attention to this transverse muscle. It is a little caricatured in 
his plates, but it is so easily demonstrated, that it is not a little 
discreditable to former veterinary anatomists that they had over¬ 
looked it. His theory of its use I understand is, that “ by the pro¬ 
gressive action of its fibres from below upwards, it assists in the ex¬ 
piration of the air in the same manner as the Successive action of the 
muscular fibres of the oesophagus from above downwards assist, or 
rather cause, the descent of the food.” Were the interior of the 
trachea surrounded by muscular fibres, or had it a proper muscular 
coat like the oesophagus, I could imagine this to be the case, yet only 
in the slightest possible degree, for we have to do with untangible 
gas, and not with a solid pellet of food ; but when we have a 
simple transverse muscle, occupying only the base of the semi¬ 
elliptical passage, and, so far as we can prove, having but little 
power in contracting the area of the tube, and I would say, most 
undoubtedly, not sufficient to produce that progressive, rapid, 
vermiform contraction of the trachea which would be required, 
I must confess that I cannot assent to this theory. 
Mr. Sewell likewise, I understand, considers broken-wind to 
be the result of paralysis of this muscle; a theory to which 1 
can by no means yield assent: but more of this in the proper 
place. 
As little disposed am I to subscribe to the hypothesis of that 
excellent veterinarian, and my esteemed friend, Mr. Percivall, 
who says that “ this self-acting band appears to him to have 
been added to the tube to enable it to enlarge its calibre.” I 
really cannot conceive how the contraction of the base of a semi- 
elliptical passage can, upon any principle of mathematics, cu- 
