298 



Veteritiaiy Obstetrics 



ward between the two lateral halves, to constitute schistoceph- 

 alus bifidns. 



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 laminae, from which the septum takes its origin. 



Fig. 35. Cleft Palatk. Foal. (From photograph). 



In some cases these margins fail to fuse 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 posterior 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 horse, 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 Eye. 



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- 



