Atresia of the Posterior Nares 1065 



atresia or closure may not end with the vulva, but may include 

 other parts of the urino-genital canal. If the vulva is com- 

 pletely closed, it prevents the discharge of urine through the 

 normal channel, and forces it to continue to pass through the 

 urachus. 



The handling of imperforate vulva cannot as a rule be suc- 

 cessful, because it is difficult or impossible to discover the 

 urethra and open it in a manner which will prove effective. The 

 animal may continue to live indefinitely with an open urachus, 

 but is of no value. When the vulva is only partially closed, and 

 there is room for urine to escape readily, there is no occasion for 

 surgical interference. As a general rule, such partial atresia or 

 absence of the vulva in reality depends upon an asexual state, 

 as is observed in freemartins, so that the animal is incapable of 

 breeding. Consequently, there is no object to be gained by any 

 surgical attempt at dilating the vulva. 



5. Atresia of the Posterior ISTares. 



In studying the development of the embryo on page 296, we 

 noted that the nasal and oral cavities are at first one common 

 chamber, which later becomes divided into two .separate pas.sages 

 by the lateral ingrowth and fusion of the palatine plates, which 

 eventually become ossified throughout most of their extent, to 

 constitute the hard palate. In some cases it is found that this 

 partition between the nasal and oral cavities continues backward 

 to the base of the sphenoid bone, thus cau.sing a more or less 

 complete atresia of the posterior nares. The defect has been re- 

 corded in man and in the horse. When involving but one 

 nostril, the defect may escape detection, because, unless the young 

 animal is caused to undergo severe exertion, the one free nostril 

 answers all demands for respiration and no inconvenience ensues. 

 If both posterior nares should be occluded, severe dyspnoea re- 

 sults, and oral breathing becomes necessary. 



When an animal, with atresia of one posterior naris, arrives at 

 a working age, and is put to heavy draft or rapid travel, the de- 

 fective respiratory passage becomes at once evident, and a dis- 

 tinct roaring noise is present. In one case existing in a three- 

 year-old in our clinic, there were no external evidences of dis- 

 ease, such as bulging or inequality of the face, no nasal dis- 



