only, and does not extend to the neural side of the vertebral column. The neural arches coalesce with the centrum; interneurals simple. The abdominal vertebræ have parapophyses, to which the ribs are attached. Only the caudal vertebræ have hæmal spines.
Fig. 40.—Heterocercal Tail of Lepidosteus.
n, Vertebral column; h, hæmal spines; dn, fulcra; dh, lower fulcra.
In the skull of Lepidosteus the cartilage of the endocranium is still more replaced by ossifications than in Polypterus; those ossifications, moreover, being represented by a greater number of discrete bones; especially the membrane-bones are greatly multiplied: the occipital, for instance, consists of three pieces the vomer is double as in Polypterus; the maxillary consists of a series of pieces firmly united by suture. The symplectic reaches the lower jaw, so that the articulary is provided with a double joint, viz. for the symplectic and quadrate; the component parts of the lower jaw are as numerous as in reptiles, a dentary, splenial, articulary, angular, supra-angular, and coronary being distinct. The sides of the head are covered with numerous bones, and a præoperculum is developed in front of the gill-cover which, again, consists of an operculum and suboperculum.
Each hyoid consists of three pieces, of which the middle is the longest, the upper bearing the largest of the three
