THE BATEACHIA OF NORTH AMERICA. 233 



Vertebral bodies uudivided, separate proatlas wanting. Vertebrae 

 very few, ou account of the anterior attachment of the pelvis aud the 

 disappearance of some aud fnsiou into a single styloid bone (the uro- 

 style) of others of the vertebrae posterior to the point of attachment. 

 Eibs very short or wanting. 



Coracoid, clavicle, and scapula osseous, well developed 5 procoracoid, 

 epicoracoid, and suprascapula cartilaginous. Sternum present, entirely 

 posterior to the coracoids. No prtBsternum nor interclavicle, but fre- 

 quently a median element anterior to the clavicles called the omoster 

 num. 



Pelvis consisting" of the usual three elements, the inferior pairs closelj'" 

 united, forming a compressed body without obturator foramina. Ilium 

 subcylindric, very elongate. 



Humerus without distinct head proximallj", but with iin epiphysis. 

 Distally a globular condyle. Other long bones with epiphyses at both 

 extremities. Astragalus and calcaneum elongate, forming a limb seg- 

 ment. Carpal bones well developed, some of them, especially of the 

 distal series, confluent. Tarsals of the distal series much reduced in 

 size aud numbers. (Plates 47, 59, etc.) 



The auditory appendages differ from those of the TJrodela, Proteida, 

 and Trachystomata in their greater 'complexity. There is a cavum 

 tympani or external ear aud a series of ossicles and cartilages extend- 

 ing through it, structures all wanting to the orders mentioned. The 

 stapes is, like that of those orders, an oval disk, which has no continu- 

 ous process, but gives origin at its middle to the stapedius muscle. 

 Immediately in front of it there arises an osseous rod, the interstapedial 

 bone. Its base is cartilaginous, and is expanded with concave surface 

 fitting the convex surface of the skull. This rod terminates at the su- 

 perior interruption of a flat annular cartilage {Annulus tympanicus), 

 which lies on the quadrate cartilage and over the concavity formed by 

 its forwards flex:ure. The mesostapedial cartilage is attached by a point 

 on its interior face to the apex of the interstapedial, somewhat as an 

 anther of a flower is attached to its filament. Its superior portion is 

 shorter, and is connected with the quadrate above by the mesostapedial 

 ligament. Its inferior portion is more or less expanded distally. Its 

 external face is flat, and is applied to the inner side of the disciform 

 epistapedial. The latter is applied like a lid to the annular cartilage 

 already mentioned. The mesostapedial then occupies a place between 

 the annular and the epistapedial cartilages. The membranum tympani 

 fits closely over the latter. (Plates 49-50.) 



The hyoid api)aratus differs materially from that of the orders men- 

 tioned. It can only be understood by reference to its development 

 from the larval stages. There are j^reseut in the larva a ceratohyal 

 ou each side and a first basibranchial, as in Urodela. The hypohyal is 

 connate with the former. Posterior to the basibranchial, two lateral 

 cartilaginous plates, the " hyobrauchials," meet on the middle line. 



