254 MR GOODSIR ON THE ANATOMY OF AMPHIOXUS LANCEOLATUS. 



connected by an aponeurosis, which forms a strong tendinous arch at the point in 

 front, where the muscles separate more completely. The whole cavity of the 

 trunk, which is occupied by the intestinal tube, is lined by a fine aporieurotic 

 membrane, which, about the lower edge of the lateral muscles, becomes muscular, 

 and shuts in the whole of the inferior part of the trunk from the mouth to the 

 tendinous arch formerly described. This abdominal muscle consists of two layers 

 an external, apparently longitudinal ; an internal, transverse. 



The only muscle in the lancelet for performing a special function is a flat 

 bundle, connecting and bringing together the two halves of the hyoid apparatus, 

 for the purpose of closing the mouth. 



Under the microscope the primitive fibres of the lateral muscles exhibit the 

 usual transverse strise, but are not collected into fasciculi, constituting imme- 

 diately the mass of the tissue. Transverse striae are not observable in the fibres 

 of the abdominal muscle. 



Intestinal System. 



This system appears as a tube passing nearly in a straight line from mouth 

 to anus. It consists of two portions an anterior, large and dilated, and appro- 

 priated to the respiratory function ; and a posterior, small, of pretty uniform 

 calibre, and constituting the proper digestive apparatus. The respiratory portion 

 of the canal will be described afterwards in connection with the vascular system. 

 The mode in which the digestive communicates with the branchial department of 

 the tube could not be satisfactorily made out. It appeared, however, that the 

 branchial cavity, becoming smaller, curved slightly of itself towards the left side, 

 and then proceeded directly, and without any change in its calibre, to the anus. 

 The anus is in the form of a longitudinal slit. 



There is not the slightest trace of a liver, or of any other assistant chylo- 

 poietic viscus. The gut was full of a brown granular matter, tinged, probably, by 

 a bilious secretion from the walls of the bowel. 



Respiratory System. 



This system is constituted by the anterior compartment of the intestinal tube, 

 on the walls of which a peculiar vascular arrangement exists for the aeration of 

 the blood, and the complicated skeleton superadded, for the efficient performance 

 of that function. 



In connection with the respiratory apparatus, I shall, as formerly proposed, 

 describe the splanchno-skeleton. This division of the osseous system consists of a 

 hyoid apparatus, and of a range of branchial ribs. 



The hyoid apparatus supports the mouth, and guards its entrance. The 

 mouth is in the form of a longitudinal slit, and is bounded on each side by the 

 two divisions of the hyoid apparatus. Each of these consists of seventeen pieces 



