OCR Text |
Show 28 PROF. B. C. A. WINDLE AND MR. J. HUMPHREYS [Jan. 14, space existing between neighbours in less roomy jaws. In still further shortening a torsion of certain teeth in the upper jaw takes place which always follows a very definite course. The tooth first to feel the strain in every case with which we have met is the third upper premolar, which becomes slightly oblique and then is rotated until it lies transversely across instead of along the alveolar border. The next tooth to yield is the second premolar, which is sometimes slightly oblique, the third being transverse and sometimes in further advanced cases also rotated into a transverse position. The teeth of the lower jaw exhibit no such transverse rotation. In the Bull-dog shortening does not proceed so far in the lower as in the upper, and consequently the upper canine has for its lower antagonists one or more of the premolars. Thus, in six Bull-dogs' skulls in which we noted the position the upper canine three times was over Pm. 3, twice between Pm. 2 and Pm. 3, and once over Pm. 2. In other cases the pressure for space may carry the last lower molar up on to the ramus of the jaw. Sometimes the lower jaws, instead of being nearly straight, are distinctly bowed to accommodate themselves to the curve of the teeth in the upper jaw. The following table shows the torsion of premolars in certain cases where it was well marked. Table XXXVI.-Torsion of Premolars. Dog. Bull-dog Bull-dog Bull-dog Bull-dog Bull-dog Pug Pug Pug f-bred Bull-Terrier Black-and-tan Terrier King Charles Spaniel Skye Islay Terrier Fox-Terrier Torsion. --! nearly transverse. Pm. 2 , Pm. 3 ... & oblique. „ „ transverse. Pm. 3 . Pm. 2 .,. transverse ; oblique. Pm. 2 „ Pm. 3 , & transverse. '- transverse. m' ° transverse, m' nearly so E., oblique L. Pm. 3 , transverse. Slight rotation of P m " 3V l-l nearly transverse. Pm. 3 ... oblique. |