1885-86.] Edinburgh Naturalists Field Club. 317 



not hitherto received that attention from the Club which these 

 subjects deserve. Possessing, as we do, a stretch of coast-hne at 

 many points not far distant from the city, a series of short excur- 

 sions at various intervals throughout the year might be an-anged, 

 in order to investigate the countless forms of life to be found at 

 the sea-shore. 



XIIL— NATURAL ENDO-SKELETON AND EXO-SKELETON OF 

 AMERICAN BULL-FROG (CERATOPHRYS CORNUTA). 



Prepared and Exhibited by 



Mr DONALD KNIGHT. 



(Feb. 19, 1886.) 



The skeleton which forms the hard internal part of the Frog is 

 composed partly of cartilage and partly of bone. Cartilage is 

 formed in the embryo, and is absorbed by the blood-vessels. It 

 presents under the microscope a clear, slightly granular substance, 

 with nucleated corpuscles imbedded in it, — in order of develop- 

 ment, at first represented by the notochord alone. Bone consists 

 of a dense, fibrillous, intercellular substance or matrix, in which are 

 imbedded cells that lie in cavities connected with one another by 

 fine branching canals. Bones developed independently of cartil- 

 age are very rare. In the skull the original cartilage is not so 

 completely replaced by bone as in the vertebral column, large 

 tracts of unossified cartilage persisting in the adult. Besides the 

 cartilage bones, the skull is strengthened by numerous membrane 

 bones. The vertebral column is the first part of the skeleton 

 which is developed in the embryo, then the head and limbs. All 

 amphibia possess a fenestra ovalis, with a cartilaginous or osseous 

 columelliform stapes, the expanded proximal end of which is fixed 

 to the membrane of the fenestra. In many batrachia, if not in all, 

 there is a fenestra rotunda, though the presence of a distinct cochlea 

 has not been ascertained. The nerve of hearing arises from the 

 side of the medulla, immediately behind and close to the root of 

 the facial nerve. It enters the audit capsule, and ends in the in- 

 ternal ear. 



I prepared a considerable number of skeletons of the common 

 American Bull-frog a few years ago, but found no exo-skeleton 

 plates present. The Ceratophrys cornuta is the only BuU-fi-og on 

 which I have found these plates ; and, so far as known to me, they 



VOL. I. Y 



