— 43 — 



In 45 mm Scorpaenas the basisphenoid is just beginning to form, appearing as a thin gutter- 

 shaped lamina of bone in the midst of the dense fibrous tissues which form the floor of this part of 

 the cranial cavity and the roof of the anterior portion of the myodome. Immediately anterior to 

 this httle bone there is a small median nodule of cartilage which lies between the extreme hind ends 

 of the recti inferior muscles, imbedded in the anterior end of a median vertical band of tough fibrous 

 tissue which gives origin to those muscles and will be further described when describing the myodome. 

 This little nodule of cartilage is connected, antero-ventrally, by a delicate median line of cartilage, 

 with the nodule of cartilage on which, in the adult, the pedicle of the basisphenoid rests, and this 

 latter nodule is connected anteriorly, also by a delicate line of cartilage, with the cartilage of the 

 interorbital septum. The pedicular line of cartilage together with the dorsal nodule thus form a 

 basisphenoid cartilage which must certainly be the somewhat reduced homologue of the transverse 

 prepituitary bolster of Amia. The basisphenoid bone of the adult Scorpaena is thus probably a peri- 

 chondrial ossification related to this basisphenoid cartilage of the young Scorpaena, but it certainly 

 extends beyond the cartilage, into the adjacent tissues, these tissues representing, in part at least, 

 parts of the primary membranous cranium that have not chondrified. 



P E ö T I C. 



The proötic (petrosal) has lateral and orbital surfaces, the former forming a considerable 

 part of the side wall of the brain case, and the latter a small part of the hind wall of the orbit. 

 The bone is bounded dorsally by the sphenotic and pterotic, antero-mesially by the alisphenoid, and 

 posteriorly by the exoccipital and basioccipital ; with all of which bones it is either in contact or in 

 synchondrosis. Its hind edge is, in part, slightly overlapped externally by the anterior edge of the 

 opisthotic. Its ventral edge is overlapped externally by the lateral edge of the parasphenoid. The 

 prepituitary portion of its mesial process suturates with the basisphenoid and alisphenoid. 



The angle separating the lateral and orbital surface of the bone forms the ventral portion 

 of the postorbital process of the skull, and on the dorsal end of this part of the bone lies the ventral 

 portion of the anterior articular facet for the hyomandibular. The hind edge of this facet is raised 

 to form a ridge which ends, at the dorsal edge of the bone, as a pronounced process, and this process, 

 as already stated, gives origin to certain of the levator muscles of the branchial arches. The process 

 lies between the articular facets for the anterior and posterior heads of the hyomandibular, and 

 abuts against the inners urface of the hyomandibular between its two articular heads, the hyomandib- 

 ular being often here perforated by a circular opening due doubtless to wear. Immediately posterior 

 to the ridge and process, there is, on the lateral surface of the bone, a marked depression or pit, 

 which, as already described, also gives origin and lodgment to certain of the levator muscles of the 

 branchial arches. In one specimen the pit was unusually deep, and at the bottom of it there was a 

 smaller pit, which gave Insertion to one of the levator muscles, doubtless the internus anterior. 

 This smaller pit in this one specimen extended forward into the postorbital process, and perforating 

 the proötic, near its edge, was bounded mesially by the sphenotic, a thin plate only of that bone 

 separating it from the cerebral recess for the anterior semicircular canal. 



The angle that separates the lateral and orbital surfaces of the proötic is traversed by a 

 canal which is the homologue of the more extensive trigemino-facialis chamber of my descriptions 

 of Scomber. The nervus facialis issues from the posterior opening of this chamber, and the trige- 



