PISCES 231 



the dorsal, scapular region, by three facets serving as attachments 

 for the three basal portions of the pectoral fin, while the supra- 

 scapula connects the scapula with the crest of the vertebral plate. 

 The pelvic girdle is not attached to the vertebral column. In the 

 male the claspers are connected closely with the posterior part of 

 the hind limb and have a complex cartilaginous skeleton and an 

 associated gland. 



Cavities. — The coelom in the trunk is divided into a pericardial 

 cavity, lined vf ith. pericardium consisting of coelomic epithelium and 

 connective tissue, while the abdominal cavity is lined with peri- 

 toneum. In the dorsal neural cavity is found the central nervous 

 system. 



Digestive System. — The mouth has teeth (special development 

 of dermal teeth) which are worn away at the outside and renewed 

 on the inside. A naso-buccal groove connects the nostrils with the 

 buccal cavity, while the spiracles which communicate with the 

 buccal cavity ventrally, open dorsally behind the eyes. The tongue 

 is reduced or almost entirely absent, in skates but is present in 

 sharks. Salivary glands are lacking, but the short broad esophagus 

 has mucus glands which lubricate it somewhat. The U-shaped 

 stomach (see Figure 109) is divided into cardiac and pyloric regions. 

 The sfnall intestine is extremely short and receives the secretions 

 from liver and pancreas. The three lobed liver has a large gall 

 bladder, leading by the bile duct to the small intestine. The 

 pancreas at the end of the duodenum, has its duct opening opposite 

 the bile duct. The colon is rather large and has a well developed 

 spiral valve, in which the mucous layer of the large intestine is so 

 coiled that it increases surface for absorption and retards the passage 



of the food. 



The rectal gland, possibly with an excretory function,^ is at the 

 posterior part of the intestine. The spleen, a ductless gland, dark 

 red in color, is attached to the stomach by mesentery but has no 

 digestive significance. It is functional in blood formation. 



Respiratory System. — The spiracles open dorsally, each con- 

 taining a rudimentary gill on the anterior wall supported by a 

 spiracular cartilage. Water may enter or leave the mouth. The 

 spiracles serve as intakes for the respiratory stream and also as 

 spout holes to clear away debris and to keep the eyes clean. ^ 



2 Crawford, J. 1899. On the rectal gland of the Elas-mobranchs. Proc. Roy. 

 Soc. Edinburgh, vol. 23, pp. 55-61. 



3 Rand, H. W. 1907. Amer. Nat., vol. 41, p. 285. 



