1820.] Physical Science during the Year 1819. 103 



that class, by what are denominated the opercular bones ; the 

 opercular bone he calls Stapes; the subopercule, Os lenticulare: 

 the mteropercule, Malleus; and a bone placed beneath the sub- 

 opercule, he names Incus. 



The next subjects of comparison are the Breast bone, and the 

 Os h I/O ides. 



His descriptions of the Sternum, and his observations on it, as 

 far as they relate to the mammalia and birds, and in part to the 

 reptiles, are sans critique; while those on the sternum and os 

 hyoides of fishes are irreconcileable. 



Dr. Leach, who has considered the subject, is of opinion that 

 the part named os hyoides of fishes, by Cuvier, in his Regne 

 Animal, is perfectly analogous to the same pail so named in 

 mammalia and birds. GeofFroy, however, refers the Apo-hyal 

 and Cerato-hyal of these animals to the sternum, merely from 

 their being the bearers of those bones that support the branchi- 

 cstegous membrane, which he compares to the sternal ribs. He 

 at the same time calls two bones that are interposed between the 

 basi-hyal and the apo-hyal, apo-hyal and cerato-hyal. We 

 suspect what these bones represent ; but until we find de- 

 cided proof, think it better to be silent on the subject. 



Dr. Leach is further of opinion that those bones in fishes, 

 which are named by Geoffioy the anterior and posterior thyreal 

 and arythyreal, which support the gill arches, are in fact sternal 

 bones, and represent the hyposternal, entosternal, and posterior 

 bones of the sternum. Dr. Leach has also very strong reasons 

 to suspect, that the criceals of GeofFroy may turn out to be the 

 zyphoids of the same part. He thinks too, that some bones in 

 the vicinity of the sternum in ornithorhynchus are likewise mis- 

 understood ; Geoffroy's Acromiuni, he believes to be the true 

 Clavicles : the Clavicles of Geoffroy to be the Episternal; and 

 Geoffroy's Episternal to be the Hyposternal. 



Dr. Leach is perfectly assured that the supposed exserted 

 Coroco'/d of Geoff i-oy, in 'Silurus, is no more than the thumb of 

 the pectoral fins in a high state of development ; if this be not 

 the case, he would ask ; where then is the thumb, and how can 

 the theory stand, if any part be actually wanting ? 



The Scapula of fishes Geoffroy has shown to be composed of 

 two bones in adult fishes, as is the case in young mammalia. 

 Dr. Leach has found the smaller of these bones, the Omo/ite of 

 Geoff"roy, to consist of two bones, in a carp of more than 20 years 

 old, and has since ascertained the same to be the case in the 

 very young foetal state of the human subject. 



The book contains a vast number of new observations made 

 generally with great accuracy, but for the most part the theory 

 is vague and hasty. It has, however, opened a wide and a new 

 field, and, if followed up, will ultimately lead to a more complete 

 knowledge of true comparative anatomy; of which this is the first 

 example that has hitherto appeared. 



Dr. A. Jacob has given a paper to the Royal Society, on a 



