investing elastic tissue which enables the pieces to move on each other as by a hinge, and being approximated by the contraction of the trachealis muscle above, the ring is flattened from side to side and the channel for the passage of air correspondingly decreased. This flattening can be easily felt by the hand in the living horse. 14th, A peculiar congenital distortion of the trachea caused by the curling in of one end of each cartilage of the windpipe and the straightening out of the other. This occasionally proceeds so far that the gullet is lodged in the interspace overlapped and hidden by the free ends of the cartilages, the diameter of the windpipe being proportionately diminished. Distortions and fractures are usually overlooked by veterinarians but from the frequency with which the author has met with them in his dissection he is convinced that they deserve greater attention than has been awarded them. 15th, Percivall records a case of inveterate _roaring_ in which, even tracheotomy having failed to cure, the patient was destroyed and the lungs found to be extensively consolidated, many of the air tubes having been so compressed as to be almost impervious. I have known a case of roaring from the presence of a pedunculated tumor in the lower end of the windpipe where it divides to enter the lungs, and the same result may ensue from the partial obstruction of the bronchial tubes by masses of tenacious mucus in chronic bronchitis. 16th. The immediate cause of _roaring_ in the immense majority of cases is the =paralysis and fatty degeneration of certain muscles on the left side of the larynx=. The muscles supplied with motive power by the =left recurrent laryngeal nerve= (Crico-arytenoideus posticus, Crico-arytenoideus lateralis, thyro-arytenoideus, and the left half of the arytenoideus) are those constantly and exclusively affected, while those supplied by the _superior laryngeal nerve_ (Crico-thyroideus, hyo-thyroideus and hyo-epiglottideus) remain unchanged. The left recurrent nerve is also wasted and considerably attenuated as compared with that on the opposite side. The _modus operandi_ of this paralysis and wasting in the production of _roaring_ is beautifully seen when the upper part of the windpipe is laid open so as to expose the interior of the larynx in laryngectomy. The triangular opening of the glottis is seen fairly dilated while the muscles are relaxed in the act of expiration. As soon, however, as inspiration commences the left arytenoid cartilage slides completely into the passage, its lower border projecting so much to the right that it forms a prominent crest extending beyond the median line and in some cases closely approaching the right wall of the larynx, the superior elastic and free border of the same cartilage meanwhile gets drawn inward by the suction power of the air so as to block up the passage still more. The closure of the glottis being thus seen to be largely controlled by the current of