RE S P IE A T ION IN T HE < ' II E I- N I A 13 



hall', while those capping the inner portion are fewer in number and reticulated, 

 permitting the lung to be seen through their interspaces. (See Fig. 3, r.) The 

 part of the muscle which arises from the vertebrae covers that triangular surface 

 of the lung which looks towards the interpulmonary notch, while that of cestui 

 origin spreads over the anterior face of the lung, sheathing its entire thickness 

 when the organ is fully inflated. A lew of the fibres capping the anterior and 

 superior extremity of the lung continue their course over the under surface of that 

 organ, spreading fan-like towards its outer edge, and being inserted into its adherent 

 peritoneal covering. They are represented by the dotted lines (Fig. 3, h). These 

 fibres are much more largely developed in some other genera, and seem to have 

 the power of drawing the lung in towards the spine, and keeping it well under tin- 

 viscera when compressed during expiration. 



The inspiratory muscles (Fig. 3,.//'') are to be sought for in the flank spaces at 

 the under and posterior portion of the trunk, into which the hind limbs of the 

 animal are drawn during repose. There is one muscle in each flank, superficial, 

 and readily displayed, by reason of the loose cellular connection it has with 

 the tissues concealing it, Turning aside the skin and fascia loaded with adipose 

 matter, as it often is in this locality, we at once expose this beautiful sheet of mus- 

 cular fibre, during contraction, stretching like a drum-head over the entire space, 

 and fitting closely its irregular boundary. Through its centre, from before back- 

 wards, runs a flat tendon (Fig. 3,/"), averaging in width one-sixth of the breadth 

 of the muscle, and receiving throughout its length, on both sides, the insertion of 

 fibres. It is usually a single band, but in several specimens we found it irregularly 

 double, being divided by islets or patches of muscular fibre. In some form, 

 however, it exists in all Chelydra, and constitutes a striking feature of the muscle, 

 its white pearly hue contrasting boldly with the crimson fringes between which it 

 is placed. In some families it loses its significance, dwindling to a central raphe, 

 or more rarely is absent altogether. The direction of the muscular fibres is 

 transverse, especially in the anterior part of the space; behind and outside of the 

 tendon they diverge to accommodate themselves to the circular sweep of the 

 carapace. Being attached to no other mobile part than the central tendon, we may 

 consider that as their insertion ; their origin embracing the entire circumference of 

 the space. Beginning with the posterior sternal bone, we may trace its fibres coming 

 from the inner edge of the plastron, where it curves around the flank, from within 

 the marginal plates of the carapace, from the fascia filling the space posterior to the 

 sacrum, and along the pelvic muscles from a ligament, the counterpart of Poupart's 

 ligament in man, stretching between the ilium and pubis. The fibres arising from 

 the anterior end of this ligament underlie the lowest fibres from the plastron, and 

 give to the latter a falciform appearance, represented in (Fig. 3, /"'). On the upper 

 side, the inspiratory muscle is attached by cellular tissue to the posterior belly of 

 the muscle of expiration, and by the contraction of this latter muscle during the . 

 expulsion of air from the lung, is carried downwards and forwards into a strongly 

 concave position, most favorable for its own subsequent effort. 



The capability of the turtle to hold the air in its lung at will, or when sub- 

 jected to great, external pressure, as must constantly occur in marine species, 



