TOWER, PRODUCTION OF SOUND IN CERTAIN FISHES 151 



of fishes having no pneumatic duct. Thus the "oval" and the pneumatic 

 ducts serve tlie same physiological function. Adhering to a portion of the 

 dorsal surface of the air-bladder, just posterior to the point of attachment 

 to the vertebrae in the male, is the central tendon of the two red drumming 

 muscles.^ Upon opening the bladder of the drum, there is found on the 

 inside, running almost the entire length, the red vascular body vv'hich has 

 been described as the blood gland, or "red body." 



Squeteague {Cynoscion regalis). — In the squeteague the swim bladder 

 (fig. 1) is a long carrot-shaped organ, tapering to a point at the posterior 

 end, and sending out from the broad anterior end three diverticula — 

 two lateral horns and a central rounded "head." The dorsal surface of 

 the "head" is attached by its outer or fibrous tunic to the sides of the body 

 of the fourth vertebra, which broadens out to receive it. The lateral appen- 

 dages of the swim-bladder of the drum are wanting in the air-bladder of 

 the squeteague, which has nothing to mar its smooth even contour except 

 the two lateral horns already described, which arise from the most ante- 

 rior part of the organ. On the inside of the air-bladder is found the char- 

 acteristic "red-body," or "blood-gland," which is present in the drum. 

 The drumming muscles are present in the male squeteague only. Their 

 insertion is lateral in the common fascia of the rectus abdominis muscle, 

 about a half-inch from the mid-ventral line. The muscles, one on either 

 side, are bilaterally symmetrical and originate from a central tendon, which 

 lies free in the mid-dorsal line just above the swim-bladder and between it 

 and the kidney. The anterior extremity of this central tendon is inserted 

 by its middle third into the dorsal surface of the neck of the swim-bladder, 

 while the right and left thirds merge into the fascia that support the peri- 

 toneum. Posteriorly, in the region of the anus, the tendon narrows down 

 to a cup-shaped extremity that receives the tip of the swim-bladder, and 

 then gradually tapers to a point, which is inserted into the base of the first 

 anal fin-ray. A closed cavity is thus formed, bounded laterally by the two 

 drumming muscles, ventrally by the confluent abdominal muscles, and dor- 

 sally by the central tendon. This closed bag or cavity contains the viscera 



' Dufossg (Annales des Sciences Naturelles, ser. V, vol. XIX. 1874, p. 39) has described in 

 Trigla lyra two red muscles which he called intra-costal muscles. From his description I am 

 unable to identify them with the "drumming muscle" just mentioned. In no case has it been 

 possible to find these "drumming muscles" in any of the Triglidce. 



Dufoss6 attributed to these intra-costal muscles the function of motor agents of the skeleton. 

 "Considgres uniquement comme agents moteurs du squelette, ces muscles intra-costaux ont 

 evidemment pour functions: d'une part, de fl6chir latSralement ou de maintenir I'gpine dorsale 

 dans sa rectitude ordinaire, suivant qu'un seul muscle se contracte, ou bien que la contraction 

 de ces deux muscles est simultange, quand les os scapulaires leur servent de point fixe; d'autre 

 part, d'attirer en dedans ces derniers os, et par suite les scapulaires et les humeraux, (Cuvier), 

 lorsque la colonne vert6brale est pr6alablement fix6e." It is evidently from this supposed 

 function that Dufoss6 gave the name of intra-costals to these muscles. 



