Prof. Owen's Description of the Lepidosiren annectens. 337 



tiire, and with the external facet concave : this I regard as the analogue of the 

 preopercular bone*: it gives attachment to the membranous and muscular 

 outer wall of the branchial cavity in which the dermal bones of the oper- 

 culum are developed in ordinary tishes. 



A strong- cylindrical and almost straight styloid bonet is articulated by a 

 somewhat compressed and expanded upper extremity to the cartilaginous 

 petrous element of the temporal ; it extends downwards and forwards, parallel 

 with the OS tympanicum, and is articnlated to the npper part of the expanded 

 posterior extremity of the cerato-hyoid bone:}:. Tlie opposite extremity of the 

 hyoid is united by ligament to the corresponding bone of tlie other side, and 

 thus comjjletes the hyoidean arch : there is no representative, bony or cartila- 

 ginous, of the body of the os hyoides. The slender cartilaginous arches of the 

 gills are merely attached to and supported by the membrane of the cavity of 

 the mouth. 



The scapular or pectoral, like the hyoidean arch, is simply composed of a 

 pair of elongated incurved bones, representing the anchylosed scapula and 

 coracoid§,on each side. The coracoids meet below the pericardium, and their 

 inferior extremities ai'C united by strong ligaments ; the scapular part, as it 

 bends upwards toward the occipital region of the skull, is expanded, com- 

 pressed, and concave towards the internal and posterior aspects, where it 

 affords origin to the lateral series of muscles below the lateral line. 



The cartilaginous basis of the rudimental pectoral fin or anterior extremity || 

 is articulated to a very regular cartilaginous cavity at the posterior and near 

 the upper end of the scapular arch. About thirty joints may be counted in 

 the single soft ray which represents the skeleton of the ])ectoral member. 



The ribs ^ are thirty-six pairs, all simple, slightly curved, slender styles, at- 

 tached to the lower and lateral part of the fibrous capsule of the gelatinous 

 vertebral chord by an upper obtuse extremity, and pointed at the opposite end, 

 which projects into the intermuscular space, and from which tfie intermuscular 

 ligament is continued. They are all of nearly the same length, viz. about five 

 lines ; the posterior pairs become straighter and incline towards each other ; 

 the thirty-seventh pair of corres])onding appendages meet at their inferior ex- 



* Tab. XXIII. fig. 4 & 5, .?..?. \ lb. t. X lb. u. 



§ lb. V. II lb. fig. 4, w. f lb. X. Tab. XXIV. fig. 2, n. n. 



2 V 2 



