OR OSSEOUS SYSTEM. 69 



cornua (a,) of the os hyoides are proportionally large, and 

 support the three branchial arches (c,) on each side to 

 which the permanent gills (d,) are attached. The flat dorsal 

 portion of the scapula (^,) is thin and cartilaginous, and the 

 coracoid pieces (/,) meet in front by broad extended edges. 

 There are only three toes (h,) developed on the fore feet, 

 the two inner consisting of three phalanges, and the outer 

 of two ; and on the hind feet there are only two toes (i,) 

 each consisting of three bones. The expanded, cartilaginous, 

 iliac bones (&,) extend upwards to the sides of the vertebral 

 column, as in the plagiostome fishes, without being attached 

 to a sacrum, and the pubic bones unite with each other 

 and with the ischia, to form a transverse anterior band for 

 the support of the small legs. The condition of all parts 

 of the skeleton is nearly the same in the siren lacertina, 

 where the prolonged fish-like vertebral column has still 

 greater freedom of motion from the entire want of legs 

 and a pelvic arch ; the spinous processes of the verteBse are 

 more elevated, the coracoid bones meet by a longer sur- 

 face, the hands have four toes, there are four branchial 

 arches on each side : the body and cornua of the os hyoides 

 are very large, and the tympanic and intermaxillary bones 

 are as moveable as in a fish. The ribs are developed to a 

 greater extent in the land salamander, where they have the 

 form of straight tapering spines extending from the trans- 

 verse processes of all the vertebrae of the trunk. The arms 

 and legs which here support the trunk in a lighter me- 

 dium than in the former animals, have all their bones larger 

 and stronger, and have four toes before and behind. The 

 whole bones of the skull and face are more fixed in their 

 articulations, and the pelvic arch is more connected with the 

 sides of the vertebral column, but without forming a 

 sacrum. 



It is however in the anurous amphibia, as the common 

 frog, (Fig. 34.) that we find the most solid and fixed con- 

 dition of all the bones, and the nearest approach to rep- 

 tiles and higher classes in the structure of the different 

 parts of the skeleton. The vertebra of the tadpole are 

 formed like those of a fish, with two cup-like cavities, but 

 by the ossification and anchylosis of the intervertebral soft 

 substance, it becomes fixed to the posterior end of the 



