298 Veterifiary Obstetrics 



ward between the two lateral halves, to constitute schistoceph- 

 alus bifid us. 



In dealing with diseases of the septum nasi, its origin should 

 always be recalled and it should be remembered that, in some 

 forms of disease, fluids may collect or new tissues may develop be- 

 tween the two laminre, from which the septum takes its origin. 



Fig. 35. CivKFT Pakath:. Foal. ( From photograph). 



In some ca.ses these margins fail to fu.se and result in a cleft 

 palate, as shown in Fig. 35. In other instances the fusion ex- 

 tends too far backward a. id, passing across the pharynx, com- 

 pletely separates the nasal chamber from the mouth and pharynx, 

 constituting atresia of the po.sterior nares, by which arrest in 

 development the animal is unable to breathe through the nostrils 

 and must respire entirely through the mouth. With the greatly 

 elongated soft palate of the hor.se, which renders oral breathing 

 extremely difficult, the animal can not live if both posterior nares are 

 closed, while, if the atresia affects but one nostril, the animal 

 can breathe readily when not .severely exerted, but, if put to 

 hard work, shows extreme dyspnoea as a result of the restricted 

 breathing room. 



The Eyk. 



The eyes originate partly from the optic vesicles of the brain 

 and partly from the optic pits in the epiblast upon the sides of 

 the head. 



The optic nerve develops from the optic vesicles, which ap- 

 pear as lateral outgrowths of the fore-brain early during em- 



