Nos. IAXD2.] ANATOMY OF SCOMBER SCOMBER. 95 



represented by an embryo 47 mm. long, the facialis and trigeminus 

 are said to have become separated from each other by an out- 

 growth of the tar capsule, and the oculomotorius and opticus to be 

 enclosed, in separate foramina, between the coalesced edges of the 

 alisphenoid and trabecular cartilages. That part of the trabecula 

 that so forms the ventral half of the oculomotorius foramen is 

 said to be formed by the hind end of the trabecula, and is said to 

 represent the "so-called clinoid wall," that is, that part of the car- 

 tilaginous skull in which the basisphenoid of fishes is developed. 

 The relations of the alisphenoid cartilage of Acanthias to the 

 nervi trigeminus, oculomotorius, and opticus is thus exactly the 

 same as that of the bony alisphenoid of Scomber to the correspond- 

 ing nerves of that fish. The alisphenoid cartilage of Acanthias is, 

 however, said to give insertion to the four recti muscles and the 

 obliquus superior of the fish, and to have probably owed its de- 

 velopment to this circumstance. This is certainly not true of the 

 alisphenoid bones of either Scomber or Amia, whatever the cause 

 of the development of the corresponding cartilages may have been. 

 In Amia, in fact, it is the so-called basisphenoid that is developed 

 in connection with the insertions of certain of the recti muscles 

 (No. 5, p. 5). 



The Squamosal {SQ) lies at the dorso-lateral corner of the 

 hind end of the skull. It forms part of the lateral surface of the 

 brain case, parts of the floors of the temporal and dilatator grooves, 

 and a part of the ridge that separates those two grooves one from 

 the other. It adjoins, anteriorly, the frontal bone and the post- 

 orbital ossification ; antero-inferiorly the petrosal ; postero-infer- 

 iorly the occipitale laterale; mesially the exoccipitale ; and be- 

 tween the postorbital ossification and the exoccipitale it bounds, 

 posteriorly, the temporal interspace of cartilage. The postero- 

 inferior portion of its lateral surface is covered externally by the 

 thin, scale-like intercalar, which bone covers also the entire lateral 

 portion of the suture between the squamosal and the occipitale 

 laterale, and part of that between the squamosal and petrosal. 

 That part of the surface of the squamosal that is covered by the 

 intercalar lies slightly depressed below the level of the adjoining 

 portions of the bone, its limiting edge being, in most places, 

 sharply marked and defined. 



