Prof. OwzN's Description of the Lepidosiren annectens. 337 
ture, 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 fishes. 
A strong cylindrical and almost straight styloid bone f 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 articulated to the upper part of the expanded 
posterior extremity of the cerato-hyoid bone f. The opposite extremity of the 
. hyoid is united by ligament to the corresponding bone of the other side, and 
thus completes 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 are 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 pectoral member. 
The ribs I 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 the 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 corresponding appendages meet at their inferior ex- 
* Taz. XXIII. fig. 4 & 5, s. s. + Ib. . | t Ib. x. 
§ Ib. v. Ib. fig. 4, w. vd q IU. x. Tas. XXIV. fig. 2, n. n. 
x. 
