AND ITS APPENDAGES. 783 



corresponding with the union of the superior maxillary and the inter- 

 maxillary processes. The lower lip, like the inferior maxilla, is com- 

 pletely consolidated upon the median line, and usually shows no trace 

 of its double origin. 



In some instances, the superior maxillary and the intermaxillary 

 processes fail to unite with each other, giving rise to the malformation 

 known as hare-lip. The fissure, in cases of hare-lip, is consequently 

 situated, as a general rule, not in the median line, but a little to one 

 side of it, corresponding with the outer edge of the intermaxillary pro- 

 cess. Sometimes the same deficiency exists on both sides, forming 

 u double hare-lip ;" in which case, if the fissure extend through the bony 

 structures, the central piece of the superior maxilla, detached from the 

 remainder, contains the upper incisor teeth, and corresponds with the 

 intermaxillary bone of the lower animals. In one instance, observed 

 by Wyman, 1 the fissure of hare-lip was situated in the median line, the 

 two intermaxillary bones not having united with each other. 



The eyes at an early period are upon the sides of the head (Fig. 289). 

 As development proceeds, they come to be situated farther forward 

 (Fig. 290), their axes being divergent and directed obliquely forward 

 and outward. At a still later period they are placed on the anterior 

 plane of the face (Fig. 291), and have their axes nearly parallel and 

 looking directly forward. This change in situation is effected by the 

 more rapid growth of the posterior and lateral portions of the head, 

 which enlarge in such a manner as to alter the relative position of the 

 parts seated in front. 



The palate is formed by a septum between the mouth and nares, 

 which arises on each side as a horizontal offshoot from the superior 

 maxilla. The two plates afterward unite upon the median line, forming 

 a complete partition between the oral and nasal cavities. The right 

 and left nasal passages are separated from each other by a vertical 

 plate (vomer), which grows from above downward and fuses with the 

 palatal plates below. Fissure of the palate is caused by a deficiency 

 of one of the horizontal maxillary plates. It is accordingly situated a 

 little on one side of the median line, and is frequently associated with 

 hare-lip and fissure of the upper jaw. The fissures of the palate and of 

 the jaw are often continuous with each other. 



The anterior and posterior arches of the palate are incomplete trans- 

 verse partitions which grow inward from the sides of the fauces, subse- 

 quently to the perforation of the pharynx and its communication with 

 the oral cavity. Owing to the muscular tissue which the}^ contain, the 

 orifice of the alimentary canal thus becomes capable of constriction or 

 enlargement, according to its condition of functional activity. 



1 Transactions of the Boston Society for Medical Improvement, March 9th, 1863. 



