R i: SPIE A TION I N THE C H E LONI A. 27 



the plastron removed, with the exception of a rim at the bach and on each side, to 

 which remained attached the fibres of the inspiratory muscles. After a few minutes 

 the turtle expired the air in the lung. During this action, the fascia covering the 

 lungs below, and lying between the peritoneum am! the plastron, was observed to be- 

 come tense, owing to the contraction of the two sheets of muscle, which terminate 

 this tendon anteriorly and posteriorly, and rind origin in the carapace. 



Recalling the full anatomical description already given, it will be remembered, 

 that the lungs and abdominal viscera are covered outside of, and below the peri- 

 toneal sac, 1>\ a white membranous tendon, which extends across the middle line, and 

 is firmly attached to the pericardium, as well as by firm areolar tissue to the central 

 line of the plastron or lower shell. The muscular bellies arising from this covering 

 tendon, fold over the lung in front and behind. Opposite to the inspiratory muscles 

 are also areolar fibres, binding its tendon to the fascia of the expiratory muscle 

 above it. When the four bellies of this muscle, or muscles contract, the lungs are 

 acted upon directly, or by being compressed through the medium of the other viscera 

 which are, so to speak, grasped during this powerful movement. At the same 

 time, the passive inspiratory muscles are drawn up with the retreating lungs, owing 

 to the pressure of the external air, and to the close union between the two sets of 

 antagonistic muscles. Although the pericardium is also fastened to the expiratory 

 tendon, this sac is so firmly bound to the plastron below it, that it docs not appear 

 to be disturbed during expiration, unless the connecting fibres arc divided, in which 

 case the heart sac and its contents are strongly drawn from the plastron, as the air 

 is expired from the lung. 



As in the case of the inspiratory muscle, the expiratory muscle was also tested by- 

 observing its action when exposed in the living animal, and by galvanizing its fibres. 

 The purpose of this singular sheet of muscle and connecting tendon admits then of 

 no doubt. Aided by the elasticity of the lung, it empties that viscus of air, and 

 no other muscle appears to lend it any aid. 



The third period of respiratory movement is marked by the closure of the glottis, 

 and by the relaxation of the muscle of inspiration, the limbs then settling passively to 

 their new positions. Hence the general appearance of a slight expiration at the 

 end of the inspiratory act, 



It is impossible to review this account of the respiration in chelonians, without 

 being struck with the simplicity of the plan. A box containing all the viscera of 

 the chest and belly has an open space on each side, filled by a muscle of peculiar 

 form, whose contraction increases the size of the visceral cavity, and thus causes 

 air to rush into it. Within the breast-box, the lungs and visceral mass embraced 

 by a single muscle, obey its contraction in effecting expiration, and as the visceral 

 cavity thus becomes smaller, the inspiratory flank muscles curve in to fill the gap. 

 After the most careful investigation, we can discover no other respiratory muscL s 

 within the breast-box. 



The muscular apparatus of the glottis is equally simple. There is a muscle to 

 open it, and another muscle to close it. Here, as in the rest of this portion of our 

 essay, we shall not commit ourselves by names, which, although they may recognize' 

 homologies, confuse the reader, who has sometimes to bear in mind that their 



