182 ANATOMY OF VERTEBRATES. 



basis, r.4, for muscular attachments, became co-expanded ; the 

 ischia also, 63, assumed the form of flattened triangular plates; 

 and the ilia, though still 'long bones,' were stronger, and attached 

 by ligament to the riblets of one or two vertebras ; and these, in 

 Nbthosaurus, became expanded for more effective fixation of the 

 pelvic arch. A ' tarsus,' 68, and ' metatarsus,' are now definable ; 

 and the ' digits,' with fewer joints, do not exceed five in number. 

 All the bones are solid in both Iclithyo- and Sauro-pterygia. 



From the Sauropterygian type of pelvic arch and limb, the 

 transition is easiest to that in the marine Chelonia of the present 

 day. But the course of developement from the Proteus will be 

 here resumed and traced to the saltatory grade which the hind- 

 limb acquires in the Batrachian order. 



Amphiuma tridactylum, with proportionally shorter hind-limbs 

 than in Proteus (fig. 101, d), has them terminated by three toes. 

 Mcnobranclius shows four toes : and Menopoma five, which is the 

 number usual in the hind-limbs of Newts and Salamanders. In 

 Menopoma, fig. 43, the sacral vertebra, s, has a longer and 

 stronger transverse process, t, and riblet, pi, than the vertebra? 

 before and behind ; and pi is united to the cartilaginous elements, 

 63 and 64, closing the inverted arch by the rib-like continuation, 62. 

 To the lower end of this simple ' ilium ' and conjoined part of the 

 * ischio-pubic ' cartilage is ligamentously attached the short and 

 simple femur. To this succeeds a shorter tibia and fibula — the 

 latter reminding us of the plesiosaurian fibula, by its outward 

 curve. The tarsus is cartilaginous in Menopoma ; the metatarsals 

 support 1, 2, 3, 3, 2 phalanges, respectively, from the innermost, I, 

 to the fifth, v. The toes are webbed to near the last joint. Every 

 joint in the limb is syndesmotic, and the ossification of the bones is 

 limited to an outer crust, covering persistent solid cartilage. In 

 the decomposing body this dissolves away ; and if the ossified 

 parts become petrified, the fossil bone appears to have had a large 

 medullary cavity. 



In the Land-salamander the broad ischio-pubic plate, fig. 113, 



becomes ossified at b, but remains cartila- 

 ginous at the angles c, and the symphysis ; 

 whence it extends forward, and bifurcates, 

 as at d, representing the last pair of abdo- 

 minal ribs in higher reptiles. There is a 

 vascular perforation in each pubic part of 

 the plate. The ilium, «, retains its simple 



Pelvis, Salamander. *i vi i 



rib-like character. 

 The Tadpole, fig. 42, affords a significant example of the trans- 



