ANATOMY OF VERTEBRATES. 83 



epicranial bone, ib. ii ; the outer side of the process is excavated 

 for the reception of the outer and anterior process of the super- 

 temporal bone. This bone, fig. 41, 12, in connection with the 

 ascending process of the maxillary, ib. 20, forms the ujjper part 

 of the orbit, and behind this connection it sends out the post- 

 orbital process, beyond which it extends Ijackward, freely over- 

 hanging the fronto-occipital, and gradually decreasing to a 2)oint, 

 and giving attachment to the anterior end of the great dorso-lateral 

 muscles of the trunk. This bone is flat above like a scale, and 

 from its superficial position might be classed with the dermal 

 skeleton : the strong temporal muscle is attached to the two 

 suri'aces, divided by the ridge on its inferior part : it is movable 

 up and down upon its anterior ligamentous union. It represents 

 the postorbital and supratemporal bones in Ganoccjihala. 



Each ramus of the lower jaw is composed of an articular, ib. 29, 

 and a dentary, ib. 32, piece, the latter anchylosed together at the 

 symphysis, and completing the tympano-maudibular arch. The 

 articular piece is a simple slender jilate, strengthening the outer 

 part of the articular concavity of the jaw, and closing the outer 

 groove of the dentary, along which it is continued forward to near 

 the symphj^sis, where it ends in a point. The articular trochlea is 

 formed by the persistent cartilage. The dentary piece has the 

 notched and trenchant dentinal plate anchylosed to it, and sends 

 ujj a strong coronoid process. Serial homology guides in the 

 determination of the special one of the part of the upper jaw to 

 which the dentary is opposed. Behind the tympanic is the pre- 

 opcroular, fig. 41, 34. The ceratohyal, 40, is suspended to the 

 petrosal cartilage close l^ehind the tympanic pedicle ; it joins its 

 fellow below without the intervention of a basihyal : it supports a 

 branchiostegal ray, 37. 



In the Ganocefhala the head was connected by ligament, as in 

 the Protopteri, to the vertebral column of the trunk, and chiefly 

 by the basioccipital part. The temporal vacuities were more 

 completely roofed over by bone, including the postorbital and 

 supertemporal ossifications. 



§ 29. Skull of Batracliia. — In modern members of this order 

 the ossification of the skull, like its chondrification in Plagiostomi, 

 is simplified, or so continuous as to indicate but obscurely its essen- 

 tially segmental character : and this condition will be noticed 

 before entering upon the description of the complex and instruc- 

 tive osteology of the head in the more specially developed and 

 divergent cold-blooded Vertebrates, called ' bony fishes.' 



In Batracliia the plagiostomous articulation of the head to the 



