XIII 



PHYLUM CHORDATA 



195 



BPTG 



PTG 



There is no pelvic girdle, its place being taken by a large, flat, 

 triangular bone, the basi-ptery giiim (Fig. 816, B. PTG.), probably 

 representing fused proximal pterygiophores : to its posterior border 

 are attached three partly ossified nodules, 

 the distal pterygiophores (PTG.), and with 

 these the dermal fin rays are articulated. 

 The adipose lobe of the pelvic fin is sup- 

 ported by a small scale-like bone. 



The muscles of the trunk and tail are 

 arranged, as in the Dog-fish, in zigzag myo- 

 meres : there are small muscles for the fins, 

 and the head has a complex musculature 

 for the movement of the jaws, hyoid, oper- 

 culum, and branchial arches. 



The coelome is divisible into a large 

 abdomen (Fig. 817) containing the chief 

 viscera, and a small pericardial cavity, situated 

 below the branchial arches, and containing 

 the heart. 



Digestive Organs. The mouth (Figs. 

 807 and 817) is very large, and has numerous 

 small recurved, conical teeth, borne, as already 

 mentioned, on the premaxillas, maxillae, pala- 

 tines, vomer, dentaries, and basi-hyal. They 

 obviously serve merely to prevent the escape 

 of the slippery animals used as food and 

 are of no use for either rending or chewing. 



The pharynx (ph.) is perforated on each side by four vertically 

 elongated gill-slits, fringed by the bony tooth-like gill- rakers. 

 Each gill-slit is V-shaped, the epi-hyal being bent upon the 

 cerato-hyal so that the dorsal and ventral moieties of the 

 branchial arches touch one another when the mouth is closed. 



The pharynx leads by a short gullet (gul.) into a U-shaped 

 stomach (st.\ consisting of a wide cardiac and a narrow pyloric 

 -division : between the latter and the intestine is a ring-shaped 

 pyloric valve. The intestine passes at first forwards as the 

 duodenum (du.\ then becomes bent upon itself (int.) and passes 

 backwards, without convolution, to the anus (an.). Its posterior 

 portion has the mucous membrane raised into prominent annular 

 ridges which simulate a spiral valve. 



The liver (Ir.) is imperfectly divided into right and left lobes, and 

 there is a large gall-bladder (g. U.). Opening into the duodenum 

 are about forty blind glandular tubes, the pyloric cceca (py.c.). 

 There is a large spleen (spL) attached by peritoneum to the fundus 

 of the stomach. The stomach, duodenum, and pyloric caeca are 

 surrounded by loose folds of peritoneum loaded with fat. 



Lying below the kidneys and extending the whole length of the 



o 2 



FIG. 816. Salmo fario. 



Skeleton of left pelvic 

 fin, dorsal aspect. 

 B. PTG. basi-ptery- 

 gium ; D. F. R. dermal 

 fin-rays ; PTG. distal 

 pterygiophores. 



