In other Sharks and in the Rays (fig. 496, 1, 2, 3, 4, andfig. 500, 3, 4, 5) the ossification of these pieces is very imperfect; the branchi, in the latter more especially, being al most entirely sustain ed by membranous structures.
The pharyngeal bones in- the irue Chondropterygii are totally wanting.
In some Sharks, as, for example, in Galeus, there are ves tiges of a true sternum situated below the branchial apparatus, from the anterior edge of which it is sus pended by ligamen tous attachments, while posteriorly it is connected with the centre of the zone, to which the pectoral fins are attached. To the sides of this ster num are appended five or six pairs of sternal ribs, but the ossification of these bones, as well as of the sternum itself, is very incomplete.
The vertebral co lumn of the cartilagi nous Fishes presents two or three very remarkable peculiari ties. In the Ray-tribe (fig. 500, 6) all the vertebrx of the ante rior portion of the spine for a considera ble distance are im moveably fixed toge ther by an incrusta tion of earthy matter that forms a kind of tube or sheath in which they are en cased, the number of vertebrm thus anchy losed to each other be ing only indicated by the foramina through which the spinal nerves make their es cape.
Another peculiari ty is that both in the !Sharks and Rays 'there are twice as many superior bral laminw as there are vertebrm. This is owing to the develope ment of spinal laminT to cover the interverte brat spaces, in addition to those which constitute the spinal canal in other vertebrata.
To the transverse processes of the vertebrte covering the abdomen rudiments of dorsal ribs are appended. In the Raidx, however, these are very small ; but in Sharks, (fig. 496, m,) and more especially in the Sturgeons (fig.499, b, c,) they attain considerable dimensions.
Along the whole length of the post-abdo minal region of the vertebral column there are developed hmmapophysial arches and infe rior spinous processes, but the latter are always exceedingly short and imperfectly formed. This is well seen in the Sturgeon (fig. 498), in which fish, although the central portion of the vertebral column remains permanently cartila ginous, the hmmapophysial arches and spines are distinctly bony.
There are no interspinous bones, the dorsal and anal fins being only connected to the spinous processes of the vertebrm by broad ligamentous expansions. The structure of the caudal fin is likewise very different from what is met with in the osseous Fishes. In the Sharks and Sturgeons, (fig. 498,) which have the tail deeply furcate, the vertebral column is conti nued into the upper portion along its entire length, the caudal fin being entirely supported by long rays connected both superiorly and inferiorly to the extremities of the spinous processes of the individual vertebrw.
The framework to which the anterior extre mities or pectoral fins are attached is a strong osseous zone which encircles the body imme diately behind the branchial apparatus. This zone consists superiorly of the scapular and supra-scapular pieces, and inferiorly of a broad osseous belt (fig. 497, k,) which encloses the fore part of the abdominal cavity, representing the coracoid and clavicular apparatus of the Reptilia. In the the supra-scapular pieces are inseparably connected with the spinous processes of the dorsal vertebm, but in the different races of Sharks they are loose and unattached. At the junction betvveen the dorsal and abdominal portions of the above zone are attached by strong articulations the pieces which support the rays of the pectoral fin. These pieces lepresent the whole brachial and carpal apparatus of the higher Vertebrata. In the Rays these are of enormous dimen sions, (fig. 500, 8, 9, 10, 11) extending pos teriorly so as almost entirely to surround the cavity of the abdomen, whilst anteriorly they are prolonged in a similar manner in front of the cranium. To the external aspect of this vast carpus are attached upwards of a hundred fingers supporting the enormous pectoral fins, which here form by far the greater portion of the body, giving it that square shape for which these Fishes are so rernarkable. Towards the circumference of the body each of the fin-rays bifurcates (12), so that the total number of phalanges entering into the composition of this prodigious hand is one of the most remarkable facts in comparative osteology.