SKELETON OF LEPIDOSTEUS. 81 



only, and does not extend to the neural side of the vertebral 



dh 



Kg. 40. — Heterocercal TaU of Lepidosteiis, 

 M, Vertebral column ; A, hsemal spines ; dn, fulcra ; dh, lower fulcra. 



column. The neural arches coalesce with the centrum ; inter- 

 neurals simple. The abdominal vertebrae have parapophyses, 

 to which the ribs are attached. Only the caudal vertebrae 

 have haemal spines. 



In the skull of Lepidosteus the cartilage of the endo- 

 cranium is still more replaced by ossifications than in Polyp- 

 terus; those ossifications, moreover, being represented by a 

 greater number of discrete bones ; especially the membrane- 

 bones are greatly multiplied : the occipital, for instance, con- 

 sists 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 arti- 

 culary 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 praeoperculum 

 is developed in front of the giU-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 



G 



