448 



CONTRIBUTION TO THE 



The types of variation in tire first point, only distinguish groups of subordinate rank. Thus the suspensor of 

 the inaudible in the typical fishes consists of the hyomandibular (stapes), quadrate (metaptcrygoid or incus), symp- 

 lectio and mosopterygoid (quadratojugal Midler, quadrate Huxley, Elcm. Comp. Anat.). In the Mormyridm, Sil- 

 tirido; Polypleridiv, (scap. arch), and others, the symplectio is absent; in the eels of several families, both it and the 

 metaptcrygoid are wanting, reducing the suspensorium to a rod of two pieces. This condition exists in many of 

 of the rays ; in others, and in the sharks, the inferior element is wanting (Midler Stannius). An important modifi- 

 cation is exhibited by Chimmra, where the hyomandibular, which alone exists, is continuous with the cartilaginous 

 cranium, not being separated by the usual articulation. As to the opercular bones, all are wanting in the Elasmo- 

 branehs (sharks and rays), while the typical fishes possess four, viz. : preoperculum, operculum, subopcrculum, and 

 interoporculum. In many of these, however, the subopcrculum is wanting, and in the, sturgeons and many eels 

 there is no preoperculum. In Polyodon the interoperculum is also wanting. In Lepidosiren the operculum and 

 interoperculum are rudimental. In respect to this point, also, the divisions indicated arc of subordinate value. 

 As regards the development of the pterotic bone, its history is not yet sufficiently made out to enable us to under- 

 stand its value. It does not exist in those with cartilaginous cranium (ElasmobrancUii). The Elasniobraiichs are 

 well known to have the scapular arch suspended freely behind the cranium as in higher vertebrates. It is not always 

 attached to the cranium, on the oilier hand, among true fishes, for in the eels it is quite as in the sharks, and the 

 spinous iiuned Mastacembelus presents the same feature. 



The character presented by the pelvic bones and limbs seem to be of higher import. Tims all the bony fishes 

 and sturgeons Jack all the pelvic elements. In the sharks and rays they are also wanting, but two elements on each 

 side appear in the Holocephali (Uhimara), according to Leydig and Gegenbaur. In JjC.pidosiren, a large median 

 pelvic cartilage exists, but which element it represents is unknown. This is evidently a character of high signifi- 

 cance. As to the limbs, the peculiarities of Polypterus have been pointed out above. They mean nothing less than 

 the development of the elements of the arm and leg of the higher Vertebrata, which intervene between the point of 

 articulation and the distal segments, in Polypterus and flic sharks and rays. In the former, the distal segments are 

 articulated exclusively to the extremitios of the proximal pieces, which thus resemble, as well as represent, humerus 

 and femur, and render the limb pedunculated. Tho proximal pieces are not continued distally, however, into the 

 representatives of the main axis, which, as demonstrated by the admirable studies of Gegenbaur, consist, after 

 humerus, of radius, inner tarsals and metatarsals, and thumb ; in the hind limb, of the line of the tibia and inner 

 toe. This continuation is observed in the Elasniobraiichs, where, however, the divergent segments extend along the 

 sides of the proximal pieces to near, in some Rajidin quite, to the articulation with the scapular arch. In the true 

 fishes, including some of the old ganoids already considered, the divergent rays always reach this articulation, while 

 the number of proximal or basal pieces is diminished. These pieces havo boon called by Gegenbaur tho Metapte- 

 rygium (humerus), Mesopterygium, and Propterygiuni ; the first being axial, the second and third being divergent 

 from it. In Polypterus, the Propterygium and Mesopterygium are largely developed ; in sharks and rays the prop- 

 fcerygium is sometimes small, sometimes wanting, while in tho true fishes the propterygium and mesopterygium are 

 both wanting, except in Amia, Lepidosteus, and the sturgeons, where a cartilaginous mesopterygium exists, accord- 

 ing to Gegenbaur. This author finds it rudimental in young Salmonidcs and Silundce. Lastly, in the true fishes 

 the distal elements of the axis of tho limb arc wanting just as in Polypterus. 



In Dipnoi, on the other hand, we have this axis complete, or rather with greatly multiplied distal segments, and 

 with uni- or bilateral radii. The bilateral type is seen in Cerntod-iis and the acute-lobcd Crossopleryyiu, according 

 to Oiinther. Hence the limb in this order is termed by Owen, the simplest or primary type, and this proposition 

 is abundantly confirmed by the beautiful researches of Gegenbaur. The foundation for the history <> I' the gene 

 sis of limbs laid by this author, vvill ever be a land-mark in the history of modern theories of creation.* 



Important as are the characters that distinguish the several groups indicated by the different types of structure 

 of the limbs and pelvis, they do not seem to me to warrant their recognition as classes, equivalent to those of the 

 six already pointed out. Taking them together, there is a greater coherence also in the structure of the brain and 

 circulatory systems than is held to be the case with any other two of the classes adopted above. The peculiarities 

 of the limbs, important as they are, are quite similar in the want of the high specialization of their parts seen in the 

 »8w lus memoir Ueber dai Slteletder Bliedmaaser der w Irbelthlere Im Allgemelnen. etc, Jenaiache Med, Zelt«chr, Vol, v. p. 39?. 



