Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 51 



terior portion there is a marked depression, directed forward 

 downward and mesially. Opposite this depression, in the antero- 

 lateral corner of the posterior portion of the groove, there is 

 usually a small, flat and relatively wide recess, which leads forward 

 and laterally onto the dorsal surface of the postorbital ossification, 

 between that bone and the overlying anterior end of the squamosal. 

 Nothing indicating the significance of this recess could be found. 



The ledge that separates the two portions or levels of the tem- 

 poral groove is formed partly of bone and partly of cartilage, the 

 cartilaginous portion being a small, four-cornered surface of 

 cartilage which may be called the temporal interspace. The re- 

 mainder of the bottom of the groove, and also its bounding side 

 walls, are formed by parts of the frontal, parietal, squamosal and 

 exoccipitale bones, and by a small, posterior portion of the post- 

 orbital ossification. From the cartilaginous interspace a narrow 

 line of cartilage runs laterally between the adjoining edges of the 

 squamosal bone and the postorbital ossification, and another back- 

 ward between the squamosal and exoccipitale. A third line, 

 usually entirely covered by the parietal, runs mesially and back- 

 ward between the exoccipitale and supraoccipital, the interspace 

 itself being continued forward, internal to the parietal, between 

 the supraoccipital and the postorbital ossification. 



The Supratemporal Groove (sptgr) is shallower than either 

 of the other two. It opens, at its hind end, onto the posterior 

 surface of the skull, the opening lying between the dorso-posterior 

 process of the exoccipitale and the spina occipitalis. Ventral to, 

 and coextensive with its hind edge there is, on the mesial part of 

 the posterior surface of the skull, a grooved or depressed portion. 

 The lateral edge of the supratemporal groove, in its anterior por- 

 tion, curves slightly laterally and forward, the corresponding part 

 of its mesial edge curving much more strongly in the same direc- 

 tion. The groove itself thus curves laterally, at its anterior end, 

 its anterior extremity lying on a level with, and close to, the an- 

 terior ends of the two other grooves. 



In certain of the teleosts described by Sagemehl (Nos. 65 and 

 66), the supratemporal groove is indicated in all, or in a part, of 

 a depressed region lying posterior to a line called by him the 

 linea nuchae, which line is said by him to indicate the position of 



