ENDOCRANIUM, BRANCHIAL AND NEURAL CARTILAGES. 



oc.p., is a thick triangular plate with clean cut, beveled edges. The apex extends 

 forward as two diverging tendons, an.s., and the posterior angles extend backward 

 over the occipitals as diverging crests that become continuous with the ragged 

 flaring plates that represent the posterior processes, p.p. A small vertical process 

 arises from the middle of the posterior margin of the supraoccipital. (Fig. 218, n.p.) 



When seen from behind, the occipital ring presents a very striking resemblance 

 to the occipital region of a vertebrate cranium. (Fig. 218, B.) The exoccipital 

 region is heavily reinforced, and on each side a ridge extends laterally from the 

 posterior face of the exoccipitals along the posterior process. 



The haemal plates are two deep, flaring plates extending along the haemal 

 surface of the trabeculae and basilar plate. The posterior haemal processes, h.p., 

 may be regarded as a local specialization of the haemal plates, corresponding to 

 the posterior pair of haemal processes in the endocranium of mygale. They are long 



FIG. 217. Endocranium of a large 

 African scorpion, seen from the neural surface. 

 Cam. outline. X 7. 



FIG. 218. Endocranium, same as in preceding 

 figure. A. Seen from the side; B, the occipital por- 

 tion, seen from the caudal end. X 7. 



narrow plates arising about opposite the anterior margin of the occipitals. The 

 anterior haemal process, a.h.p., is a thin, irregular prolongation of the anterior 

 margin of the haemal plate. It is of uncertain form, since its margins are easily 

 injured in the dissection. 



The haemal plates converge posteriorly, following the general direction of 

 the trabeculae. The anterior ends flare outward; the posterior ends are nearly 

 vertical, and form the lateral walls of a deep sub-cranial channel in which lies 

 the posterior portion of the stomodaeum and the anterior end of the gut. In Fig. 

 218, A, the brain and endocranium are shown from the side in their proper re- 

 lations. The anterior ends of the trabeculae reach almost to the anterior surface 

 of the bent over forebrain. The neural surface of the trabeculae forms two 

 horizontal shelves on either side of the hindbrain, the four posterior thoracic 

 neuromeres sending their nerves laterally over the neural surface of the shelf. 



