216 TEXT-BOOK OF EMBRYOLOGY. 



increase occurs in the vertical and longitudinal directions. This results in the 

 vault of the skull becoming heightened and elongated, like an inverted skiff, a 

 condition known as scaphocephaly. After premature closure of the coronal 

 suture, growth takes place principally upward and gives rise to acrocephaly. In 

 case only one-half the coronal or lambdoidal suture is closed, the growth is 

 oblique and results in plagiocephaly. 



A suture — the metopic suture — sometimes exists in the medial line between 

 the two halves of the frontal bone, a condition known as metopism. This is due 

 to an imperfect union of the two plates of bone produced by the two centers of 

 ossification in the frontal region (p. 198). 



Certain malformations in the face region and in the roof of the mouth are 

 brought about by defective fusion or complete absence of fusion between certain 

 structures during the earlier embryonic stages. The maxillary process of the 

 first branchial arch sometimes fails to unite with the middle nasal process 

 (Kolliker's view, p. 200; see also Fig. 136). The result is a fissure in the 

 upper lip, a condition known as hare lip, which may or may not be accompanied 

 by a cleft in the alveolar process of the maxilla, extending as far as the incisive 

 (palatine) foramen. The same result may be produced by a defective fusion 

 between the middle nasal process and the lateral nasal process (Albrecht's view, 

 p. 2oo-; see also Fig. 136). Hare lip may be either unilateral (single) or bilateral 

 (double), accordingly as defective fusion occurs on one or both sides, but never 

 medial. 



Occasionally the palatine process of the maxillary process fails to meet not 

 only its fellow of the opposite side, but also the vomer (see Fig. 179). The result 

 is a cleft in the hard palate, a condition known as cleft palate. This malforma- 

 tion may be unilateral or bilateral, but not medial. Sometimes the cleft extends 

 into the soft palate where it occupies, however, a medial position. 



Cleft palate may accompany hare lip, or either may exist without the other, 

 depending upon the degree of fusion between the processes mentioned above. 

 In bilateral hare lip, with or without cleft palate, the incisive (intermaxillary) 

 bone is sometimes pushed forward by the vomer and projects beyond the surface 

 of the face, a condition known as "wolf's snout." 



The causes underlying the origin of hare lip and cleft palate are very obscure. 



The Appendicular Skeleton. 

 The Humerus. — On the medial side of the humerus, just proximal to the 

 medial condyle, there is not infrequently a small hook-like process directed 

 distally — the supracondyloid process. This process represents a portion of bone 

 which in some of the lower mammals (cat, for example) joins the internal 

 condyle and completes the supracondyloid foramen, through which the median 

 nerve and brachial artery pass. 



