APPENDIX. 



Since committing to the press the preceding paper, we have had the opportunity 

 of examining the respiratory apparatus of one of the Trionychidse. 1 The striking 

 characters of this family and its border rank amongst fresh-water turtles, render a 

 knowledge of its respiratory structure of peculiar interest, and constitute our 

 apology for this appendix. 



Am //da mutica, Fitz.— The general plan of arrangement of the respiratory muscles 

 is the same as heretofore described, the inspiratory muscles occupying the Hank 

 spaces, and the expiratory muscle being attached to the dorsal shield and inclosing 

 the viscera. The origin of each inspiratory muscle, in detail, is as follows: From 

 the bony edge of the plastron, from the carapace at the line of termination of the 

 ribs, from the fascia lata, where the thigh bounds the flank space, from the spinous 

 process of the ilium and thence to the place of beginning on the plastron. The 

 central tendon into which these fibres are inserted, is a mere raphse posteriorly, but 

 widens anteriorly into a lance-shaped extremity, one-fourth of an inch wide at its 

 widest part. The whole muscle is relatively large compared with that of other species 

 The expiratory muscle presents greater variation in origin and form than the inspi- 

 ratory muscle ; the fibres are longer than in other turtles examined, and the ante- 

 rior and posterior bellies broader. These bellies meet at their outer margins and leave 

 no space under the bridge of the plastron where the muscular fringe is absent when 

 the muscle is viewed from below, as exists in the snapper, Fig. 3. The effect ot this 

 widened muscular margin is to diminish the size of the common tendon, and reveal 

 its true character more strikingly than in other families. On dividing the tendon 

 and removing the viscera, the muscular fibres are observed spreading out across the 

 dorsal shield in fan-like radii from each intercostal space, from the first to the sixth 

 inclusive. The third intercostal space gives attachment to the strongest fibres, 

 causing it to appear as the centre from which the whole muscle radiates, the tibres 

 running forward and outward across the area of a quarter circle constituting the 

 anterior belly, and those running backwards over a similar area, the posterior 

 belly. More precisely, however, the origin of the anterior belly is from the 

 first .and second intercostal spaces and from the costal margin of the third space; 



1 For living specimens of Amyda mutica, we are indebted to Mr. Robert T,. Walker, of Allegheny 

 County, Pennsylvania. 



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