70 



MEMOIRS OP THE UNIVERSITY OF CALIFORNIA. 



The structure seen in Mixosaurus appears more primitive than in the other 

 forms, and seems also to show that no rearrangement of the digits has been 

 made through addition to, or subtraction from the original number. 



As to the definite relationship of the forms with the mixosaurian type of 

 paddle to the typical Latipinnati of the Jurassic, and to the more specialized 

 forms of the B(ti>t<niodon type, there may be some doubt, as the largely devel- 

 oped pisiform of Mixosaurus is not necessarily present in the Latipinnati. 

 According to Baur's view (1887, 1) the pisiform of Mi.ros((urus has ultimately 

 become the third or posterior epipodial element in Bapta notion (fig. 107). 

 There may, however, be some question as to such a transition through IchHii/o- 

 saurus. Though a small proximal element of the posterior podial row may 

 overlap the most posterior of the three elements of the first mesopodial row, 

 it is difficult to demonstrate that the large pisiform of Mixosaurus has been 

 continued through Ichthyosaurus to Baptanodon. As has been shown by Fraas 

 (1891, pp. 27 and 30), the intermedium may come into articulation with the 

 propodial element and thus furnish opportunity for development of the 

 Baptanodon type of limb in any one of several groups. Boulenger (1904) lias 

 also shown that in Ichthyosaurus extremus (fig. 108) even though it be of the 

 latipinnate type, the third element in articulation with the propodial is the 

 intermedium. It is also interesting to note that Broili 27 has recently described 

 a broad-paddled form (fig. 109) which he refers to the Longipinnati. 



Some suggestions as to the possi- 

 bility of rearrangement of the ele- 

 ments of the mesopodial region are 

 perhaps to be found also in the struc- 

 ture of the posterior limb of Mixo- 

 saurus. In the first row of the meso- 

 podial section of the hind limb figured 

 by Eepossi (fig. Ill), as in the an- 

 terior limb, four elements appeal- 

 instead of three. The structure which 

 appears in this case is unusual, but is 

 probably explained by another speci : 

 men in the Milan museum (fig. 110) 

 in which only three elements are pres- 

 ent in the proximal row. The lunate 

 intermediate element almost closes 

 the gap between the tibiale and fibulare, but in a second row of bones 

 three elements articulate with the distal border of the intermedium ; of these 

 the anterior one has crowded up between the tibiale and intermedium so as 



27 Broili, F., Palaeontog., Bd. 54, p. 151. 





no 



Fig. 110. Mixosaurus cornalianus (Bassani). Posterior 

 limb, about natural size, from rough sketch by the 

 author. T, tibia; Fb, fibula; C, a distal carpal? 



Fig. 111. Mixosaurus cornalianus (Bassani). Posterior 

 limb, natural size. (After Eepossi.) F, femur; T, 

 tibia; Fb, fibula; C, a distal carpal? 



