LIASSIC ICHTHYOSAURS. 63 



intervals between the midcarpal and the two distal carpals, which it partly supports. The 

 radial and ulnar ossicles (56', 56') of this third series from the humerus are extended trans- 

 versely ; the four of the following series articulate each with its corresponding carpal. 



The series of three bones (Tab. XXIX, fig. 1, 56) presents the same relation to the anti- 

 brachials as does the proximal row of carpals in Tesfudo ; ^ and the series of four ossicles 

 which follows may be homologised with the distal series of carpals in the same number 

 in Testudo. In this case the next transverse row of four ossicles, the third from the 

 antibrachium, may be regarded as metacarpals (.)/). According to this view the radial 

 metacarpal (57'), not the ulnar one (57) supports two digits, and the normal digits in 

 Ichtliyomurus communis are thus five in number (i, 11, iii, iv, v). Each consists of a 

 series of flattened, somewhat transversely extended ossicles, of which I have counted tliirty 

 and upwards in the two ulnar digits of the present species ; they are rather fewer in the 

 two radial and the mid-digits. But, in addition to these multiplied digital joints there 

 are two superadded marginal series of ossicles ; that (1') on the radial border of the fin 

 begins between the second and third joints of the radial digit, and is continued to near 

 its extremity. The series (v') along the opposite, ulnar, margin, begins at the interval 

 between the ulnar proximal and distal carpals, and is also continued to near the extremity 

 of the fifth normal digit. These supplementary ossicles are more rounded in shape than 

 the normal phalanges, but, like these, progressively decrease in size to the tapering end 

 of the fin. At first view, apart from the preceding homological analysis of the bones of 

 the fore limb of IcUhyosaurus, they seem to show that seven digital series are present in 

 that fin of IcTi. communis. 



All are enveloped in one sheath of smooth integument, which is continued beyond the 

 framework to an obtusely pointed end, and likewise extends some way beyond the 

 hinder or ulnar border of the bones, where it seems to have been supported by numerous 

 fine cartilaginous rays unless the appearance be interpreted as due to parallel bifurcate 

 wrinkles of the skin (Tab. XXIV, fig, 5).' 



The ilium (Tab. XXVI, fig. 5, 62) is an oblong, subcompressed bone, slightly enlarging 

 at the acetabular end to form the articular surfaces for pubis, ischium, and femur ; some- 

 times, also, more slightly expanding to the opposite free flattened end. This part, if 

 attached to any of the vertebrae, would be so by ligamentous or soluble tissue. The length 

 of the iUum does not exceed, usually, that of three contiguous centrums. 



The ischium (ib. 63), of minor length, is thickened at the acetabular end, which shows 

 facets for the ilium, the pubis, and its share in the shallow cotyloid cavity for ligamentous 

 attachment of the head of the femur. The body of the ischium expands, more or less in 

 different species, to its free non-articular border, anterior to which it unites synchoudro- 

 sally with the pubis. This (ib., Ci) is usually a somewhat longer bone; it also expands 



^ ' Ar.at. of Vertebrates,' vol. i, p. 174, fig. 108, a, d, c. 



2 ' Transactions of tlie Geological Society,' 2nd series, vol. vi, p. 199, pi. .\.x. 



