46 Mr Taylor on the Respiratory Organs and Air-bladder 



ing to the scapula to be inserted into the os hijoides. Of all 

 the arches, the second alone possesses lamina? for the purpose 

 of breathing; and these consist merely of a few long fibrils at- 

 tached to the middle of the arch, and occupying but a very 

 small extent of its surface ; the third supports in the place of 

 laminae, a thick and semitransparent tissue, which in large in- 

 dividuals of the species presents a fringed or denticulated ap- 

 pearance at its edge, while the first and fourth are bare, hav- 

 ing only the membrane that fills up the space between the. 

 arches reflected over them. The principal organs of respira- 

 tion are two small bladders, which the animal has the power 

 of filling with air, immediately derived from the atmosphere. 

 They are placed behind the head, one on each side of the neck, 

 above the superior or vertebral extremities of the branchial 

 arches, and are covered over by the common integuments, pre- 

 senting externally, when distended with air, two protuberances 

 of a round shape. On dividing the skin, and reflecting it back, 

 each bladder is found to be partially covered, at its anterior 

 part, by a small and extremely thin operculum, joined to the 

 upper part of the articular bone of the head, and connected be- 

 low with a membrana brancltiostega, which is supported by 

 six osseous rays. The posterior portion of the organ extend- 

 ing beyond the edge of the operculum, is confined in its situa- 

 tion, by a broad but thin muscular expansion, running across 

 it in an oblique direction, from the tendinous sheath of the 

 spinal muscles above, to the gill membrane below. These 

 bladders, which are smooth, and highly vascular upon their 

 internal surface, do not possess a laminated structure, such as 

 that of the respiratory bags in the lamprey ; but present, when 

 separated from their surrounding attachments, and inflated 

 with air, thin semitransparent membranous parietes resembling 

 the posterior portion of the lung of serpents. Each communi- 

 cates with the cavity of the mouth, by a wide semilunar open- 

 ing between the os hyoides and the first branchial arch ; its 

 lower margin, which is thick and prominent, is composed of 

 several muscular fibres that extend between the end of the 

 first branchial arch and the side of the spine, constituting a spe- 

 cies of constrictor muscle, by means of which the aperture can 

 be contracted to so small a size, as to perform, in some degree, 



