72 THE TONER LECTURES. 



Linear grooms of doubtful origin on the periphery. — A number of 

 grooves are seen ou the superior maxilla as it enters into the com- 

 position of the outer wall of the orbit and of the boundaries of the 

 spheno-maxillary sinus which closely resemble those caused by ves- 

 sels. They are seen as fissures in the skull of the child and as 

 linear depression in the skull of older subjects. Should they be 

 accepted as vessel-grooves, the interesting question is raised : j\Iay 

 not such irregular fissures as are here seen on the maxilla as it ex- 

 tends upward toward the orbital wall be caused by the presence of 

 vessels, and may not the irregular sinuate edges on the margin of a 

 growing bone of the flat class be generally associated with such 

 modifying causes? 



The malar bone occasionally exhibits a transverse linear groove 

 upon the middle of the inner (temporal) surface. (See page 8.) 

 It corresponds to the division between the masseteric and the tem- 

 poral surfaces as seen in the child at three years, and to the line of 

 the suture which so rarely divides the malar into two parts. 



Vessel-grooves on the encranial surface. — Among the grooves on 

 the endocranial surface of the parietal bone which are of undoubted 

 influence, the form of the surrounding parts, is the conspicuously 

 broad and deep depression which lies directly back of the coronal 

 suture. The constriction so commonly seen in the periphery in 

 this portion of the skull cannot be disassociated with the position 

 of these vessels. The nutritive processes appear to be at first stim- 

 ulated by the presence of this line of vessels, but after union with 

 the frontal bone it remains stationary and permits the adjacent por- 

 tion of the skull to rise above it. At the antero-inferior angle of 

 the parietal bone the groove is converted into a canal and the inner 

 layer of the bone notably thickened. In crania which exhibit a 

 tendency to thickening of the vitreous plate the vessel -grooves are 

 deep, sharply defined, and resemble the tracks made by insect-larvse 

 in old wood and in neglected books. The diploe is often exposed 

 at the bottom of these grooves. Doubtless the diploic vessels freely 

 unite with the vessels. 



