FISHES. 357 



arches, from penetrating into the intervals between the branchiae, 

 where it might wound organs so delicate as those of respiration. 

 The movements of the jaw and the tongue cannot make it penetrate 

 into any other way than that of the pharynx, where it again undergoes 

 a new action from the teeth of the pharyngeal bones, which triturate 

 it or cany it further back as far as into the oesophagus. 



It cannot be said that there is, in all this passage, any organ which 

 resembles the functions of the salivary glands : certainly the cyprins 

 and some other genera have the palate furnished with a thick layer 

 of a soft red substance, furnished with very numerous nerves, and which 

 are irritated by the least percussion ; it oozes, from the surface, a 

 slight mucus, from imperceptible pores ; nevertheless, I do not 

 from this circumstance, see a salivary gland, or even a gland at all. 

 It is a particular tissue, very sensible, and which is probably destined 

 to exercise an office more or less analogous to that of taste. 



The oesophagus is lined with a layer of strong muscular fibres, 

 compact, and sometimes forming various fascia, whose contractions 

 push the alimentary bit towards the stomach, and it is in this manner 

 that it is completely swallowed ; for the oesophagus of fishes is neces- 

 sarily very short in the greater part of the species, since they have no 

 neck. 



Nevertheless there is sometimes in the thickness of the walls of the 

 oesophagus a glandular substance. It is very apparent in the ray. 



The Intestinal Canal. 



The viscera of digestion are enclosed in the abdominal cavity, 

 which is separated anteriorly from that which contains the heart, by 

 a kind of diaphragm of small extent, formed of a lamina which gives 

 off the pericardium, and of another which appertains to the perito- 

 neum ; the diaphragm is deprived of proper muscles, but reinforced 

 by the aponeurotic fibres between the two lamina, and receives never- 

 theless some action from one of the muscles of the branchiae : the 

 great venous sinus occupies a part of its thickness. Another cavity 

 exists along the spine, and contains the kidneys and aerial bladder; 

 the peritoneum separates it from the abdomen properly so called, and 

 at the same time, as in other animals, it is folded within the abdo- 

 minal cavity, to embrace and suspend the viscera which it contains, 

 and which are the intestinal canal, the liver, the sjjleen, as well as the 

 pancreas when it exists. The organs of generation and the urinary 

 bladder are generally enveloped in folds of the peritoneum, and lodged 

 in its interior ; but, as we have just said, the kidneys, and even most 

 frequently the natatory bladder, are without and covered on the side 

 of the belly only, by the peritoneum. 



One thing very remarkable is that there are many fishes, such as 

 the ray, the squalus, the sturgeon, the lampreys, and the salmon, 

 which have on the sides of the anus two holes which penetrating into 

 the abdominal cavity, in such a manner that the anterior lamina of 

 the peritoneum continues with the epidermis, and appertains to the 

 order of mucous membranes ; two other holes, at least in the ray and 



