Nos. IAXD2.] AX ATOMY OF SCOMBER SCOMBER. 113 



tral edges of the maxillary and premaxillary bones, so that these 

 bones are completely covered and hidden from view by the lachry- 

 mal, excepting only at their anterior ends. As a result of its con- 

 nection with the maxillary and premaxillary bones, the lachrymal 

 has, when the mouth is opened or shut, an oscillating motion 

 around its articular facet as a centre, its motion being in an oppo- 

 site direction to that of the two bones to which it is attached. 

 This motion is communicated in part to the first post-lachrymal 

 bone, but not to the second, the sliding joint between that bone 

 and the first post-lachrymal one preventing a transmission of the 

 motion. The lachrymal is traversed by the sub- and antorbital 

 parts of the main infraorbital lateral canal, the canal ending near 

 the antero-dorsal edge of the bone, somewhat in front of the 

 articular facet. 



2. Vertebrje. 



The First Six Vertebrae of Scomber increase slightly in size 

 and length from the first to the last. They are all strongly bicon- 

 cave, and about once and a half as long as wide. The ventral 

 half of each vertebra "(Fi^- ^6) has a smooth lateral surface, 

 without process of any kind, and has the ordinary hour-glass 

 shape. The dorsal half is irregular, due to the fusion of the dorsal 

 arch with the body of the vertebra. On the dorsal surface of the 

 body of the vertebra there is a large median depression, the mid- 

 dle and deepest point of which reaches almost to the center of the 

 vertebra, the vertebra having accordingly, in median vertical sec- 

 tions, a decidedly hour-glass shape. From the sides of the me- 

 dian dorsal depression the dorsal arches arise, each arch consist- 

 ing of a slender spine, on both sides of the base of which there is 

 a broad, thin and delicate web of bone. The spine on the first 

 vertebra is much shorter than those on the others. The base of 

 each spine is thickened and broadened, and forms, on the outer 

 surface of the webbed part of its arch, a strong projecting ridge. 

 The web, on each side of this ridge, extends the full length of the 

 vertebra, and arches upward and mesially, to form, with the web 

 of the opposite side, the sides and top of the spinal canal. At the 

 anterior and posterior ends of the vertebra delicate spicules of 

 bone may unite the webs of opposite sides across the mid-dorsal 



