Prof. Owen on the Lepidosiren annectens. 73 



branchial arches, and the bodies of the vertebrae : these, moreover, are 

 not separated to correspond with the neurapophyses and ribs, as in 

 Plagiostomous Cartilaginous Fishes, but retain their primitive con- 

 fluent condition as around continuous chord, extending from the oc- 

 ciput to the end of the tail : this vertebral chord consists of an ex- 

 ternal firm, elastic, yellowish capsule, enveloping a softer subgelati- 

 nous material, as in the Cyclostomous Fishes. The corresponding 

 parts or basilar elements of the cranial vertebrae were ossified : and 

 Mr. Owen then entered upon a detailed description of the skull. 



The ribs are thirty-six pairs, and consist of short, slightly curved, 

 slender styles, encompassing, with the spine, about one-sixth part of 

 the cavity of the abdomen. The rudimental filiform pectoral and 

 ventral fins were supported each by a single cartilaginous ray com- 

 posed of many joints. 



The muscles of the head, jaws, hyoid and branchial apparatus 

 were then described : the muscular system of the body consists of 

 subvertical layers of oblique fibres separated at brief intervals by 

 aponeurotic intersections. 



The following peculiarities of the Digestive system were then 

 pointed out ; — two long, slightly curved, slender, sharp-pointed 

 teeth project from the intermaxillary bones, which are moveable. 

 The upper maxillary bones support each a single dental plate divi- 

 ded into three cutting lobes, by two oblique notches entering from 

 the outer side : the lower jaw is armed with a single dental plate si- 

 milarly modified, the produced cutting edges fitting into the notches 

 above : these maxillary teeth somewhat resemble the dental plate of 

 the extinct Ceratodus of Agassiz. The fleshy and sensitive parts of 

 the tongue are more developed than in fishes generally. The jaws 

 are adapted to minutely divide and comminute alimentary substances; 

 the pharyngeal opening is contracted ; the entrance to the pharynx 

 guarded by a soft semicircular valvular process. Gullet short, straight, 

 narrow, but longitudinally plicated. Stomach simple, straight, with 

 thick walls, in capacity corresponding with the oesophagus ; termi- 

 nating by a valvular pylorus projecting with a scalloped margin into 

 the intestine. No pancreas or spleen. Liver well- developed, partly 

 divided into two lobes. A gall-bladder, and large ductus choledochus, 

 opening by a valvular termination close to the pylorus. Intestine 

 round, straight, at first of equal diameter with the stomach, but gra- 

 dually contracting to the vent, with thick parietes ; traversed inter- 

 nally by a spiral valve describing six gyrations ; the first of which is 

 the longest. 



The respiratory organs consist of branchias, and a double elon- 

 gated air-bladder, with the usual vascular and cellular structure of 

 the lungs of a reptile. 



The branchicB consist of elongated, sub-compressed, soft, pendu- 

 lous filaments, attached to cartilaginous branchial arches ; these 

 arches are not joined together, or to the os hyoides by an interme- 

 diate chain of cartilages or bones below, nor are they articulated to 

 the cranium above. There are six branchial arches on each side, 

 and five intervals for the passage of the water from the mouth to the 



