STRUCTURES OF CHIM.-EROWS iqi 



the upper jaw (" premaxillary " and "palatine") ; they are 

 studded with hardened points, or "tritors " (Figs. 109-1 12). 

 The sense organs are similar to those of sharks ; the nasal 

 capsule, A^AS, has both an anterior and a posterior open- 

 ing, O, 0', the latter within the cavity of the mouth. 



The visceral parts are decidedly shark-like ; the diges- 

 tive tube is straight (p. 263) ; the intestine, /, with a spiral 

 valve of three turns ; the liver, L, is prominent ; the 

 kidney, K, reproductive organs, T, and their ducts, VD, 

 SS, VS, and abdominal pores are as in sharks ; the intes- 

 tine, however, opens directly to the surface. A, separating 

 an anal from a urogenital aperture, UG. The mesenteries 

 are string-like. 



The male fish is provided with a highly specialized intro- 

 mittent organ, CL ; it has a supplemental clasping organ, 

 VC, at the front margin of each ventral fin, F (cf. also Fig. 

 116 and Fig. 116^), and a retractile spine in the region of 

 the forehead, MSF (cf. Figs. 113 and 115). 



The skeleton of a Chimaeroid is shown in the following 

 figure (Fig. 105). Its structure is cartilaginous. The ver- 

 tebral axis is notochordal ; its sheath, lacking in definite 

 centra, is strengthened anteriorly by a series of calcified 

 rings. In the anterior region of the trunk, neural proc- 

 esses, interneurals, and neural spines. NP, IN, NS, to- 

 gether with haemal processes, occur as in sharks ; toward 

 the tail regfon they fade away, and before joining with 

 the head at the occipital condyles, OC, they fuse into a 

 compact mass, joining with the basal supports of the 

 dorsal fin. 



The cranium is of a highly compacted structure ; its 

 vertical height has been greatly produced ; the orbits, OR, 

 are of great size and are separated from each other by a 

 membranous septum. The snout region is greatly meta- 



