The "arrow" pattern.  [electronic resource] 

 -  Radiology  Oct 1981 
 - 270-2 p.  digital 
<br/><br/> Publication Type: Letter 
<br/><br/><label>ISSN: </label>0033-8419 
<br/><br/><label>Standard No.: </label>10.1148/radiology.141.1.270-b  doi 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Brain--embryology<br/>Female<br/>Humans<br/>Parietal Bone--embryology<br/>Pregnancy<br/>Ultrasonography