ORGANS OF DIGESTION. 383 



the stomach is abundantly perforated by the orifices of 

 muciparous follicles. As in the invertebrated classes, the 

 mesentery is often wanting or imperfectly developed in 

 fishes, especially in the chondropterygii ; the intestines are 

 suspended by ligamentous bands which afford passage to 

 the vessels, and the distinction of great and small intestine 

 is scarcely perceptible, there being no ccecum-coli, and the 

 colon preserving the same width and structure as the ilion, 

 as seen in the annexed view of the chylopoietic viscera 

 of the burbot, gadus lota (Fig. 123. B.) Immediately above 

 the heart (123. B. .) is seen the wide muscular oesaphagus 

 (123. B. b.} passing backwards over the large lobes of the 

 liver (123. B. g. g.) to the capacious stomach (123. B. c.) of 

 this fish, and close to the pyloric valve the wide duodenal 

 portion (123. B. d.) receives the ducts, rarely united in fishes, 

 of the gall-bladder (123. B. h.) and of numerous pancreatic 

 follicles (123. B. i.). The wide intestine (123. B. e. e.), after 

 forming several convolutions below the large air-sac (123. 

 B. /. /.), terminates in the fore part of the cloaca (123. B./.) 

 anterior to the common opening of the urinary organs and 

 of the two ovaries (123. B. n. n.) 



The mucous membrane of the stomach in this class com- 

 monly presents an irregular plicated surface, and that of the 

 intestine is often plicated and villous, but without forming 

 valvulce conniventes like those of higher classes. At the part 

 analogous to the caput coli, and where there is sometimes a 

 small caecum as in the sole, the mucous membrane passes 

 inwards to form a free circular valvula coli which is often the 

 only perceptible mark of distinction between the great and 

 small intestine. The colon however is sometimes distin- 

 guished both by the presence of this circular valve and by its 

 greater width, without either external longitudinal ligamentous 

 bands or internal transverse folds, as seen in Fig. 124. which 

 represents the digestive organs as I found them in the sword- 

 fish, xiphias gladius. The wide plicated muscular oesophagus 

 (124. a.) here presents strong sphincter bands at the cardiac 

 orifice (124. b.) of a long flask-shaped stomach (124. c.) 

 with thick muscular parietes, especially at the narrow cylin- 

 drical pyloric portion (1 24 . c. d.) Beyond the pyloric valve 

 (124. d.) the three hepatic ducts (124. /.) from the liver 

 (124. e.} and the cystics form an irregular lobed gall-bladder 



